IF DECK TIPS R390A IF Deck Alignment _Chuck Rippel_ R390's by qingyunliuliu

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									IF deck tips                            page 1

                                     IF DECK TIPS

                     R390A IF Deck Alignment (Chuck Rippel)

R390's made after 1954 and those with mod 2 stamped on the IF chassis have a
field change installed to the mechanical filters. Filter input and output trimmer
capacitors have been added. The 4 input trimmer capacitors are found by
removing the 2 square can on top of the IF chassis using the single nut in the top.
The 4 output trimmer capacitors are located behind 4 holes in the left hand side
of the IF deck. The IF chassis will need to be loose but still electrically connected
to complete these procedures.

An accurate counter, analog VTVM and a signal generator capable of outputting
455.00 KC, is required for these alignments.

Connect the VTVM to the Diode Load bus on the rear and configure it to read a
negative voltage of approximately -7vdc. Set the receiver FUNCTION control to
MGC, BFO to OFF and the LOCAL GAIN control to a comfortable level. Lift and
tilt the IF deck resting the front captive (green) screw over the front panel. You
should be able to gain access to the mechanical filter trimmer capacitors through
the large ventilation holes in the main chassis.

Locate the cable running from the rear of the IF deck to the *IF OUT* BNC
connector in the rear panel, upper left side. Unplug the cable from the IF deck
only. Also unplug J-513 and the one next to it. Plug the cable running from the
rear IF Out jack into J-513 on the IF deck. Connect the output of your 455.000 kc

                           Mechanical Filter Alignment-

•        Set the 455kc generator output level to cause the VTVM to read about
•        With the IF deck oriented so that the bandwidth control
         is towards you, set the bandwidth to 2Kc and align 1 of the four
         top trimmers.
•        Adjust C-569 which is at 9 o'clock for a peak on the
•        Next, align the output trimmer in the left side of the
         IF deck, labeled C-567
•        Set the BW to 4KC
•        Align the top trimmer, C-568 located at 12 o'clock
 •       Align the side trimmer, C-566 located at rear, bottom.
 •       Set the BW to 8kc
 •       Align the top trimmer, C-570 located at 6 o'clock.
 •       Align the side trimmer, C-565 located at front, top.
 •       Set the BW to 16kc
 •       Align the top trimmer, C-571 located at 3 o'clock
         Align the side trimmer, C-564 located at front, bottom.
IF deck tips                            page 2

                             IF Transformer Alignment-

 •       Select the 16KC filter
 •       Set the generator frequency to 467kc.
         Note: The generator output should be increased until the VTVM
         indicates approximately -2vdc.
         Do not be alarmed if that level is over 0.1 volts.
 •       Adjust the top slug (secondary) of T-501 for a peak
         reading on the VTVM
 •       Adjust the bottom slug (primary) of T-502 for a peak
         reading on the VTVM
 •       Set the generator frequency to 443kc. Note: The generator output should
         be increased until the VTVM indicates approximately -2vdc.
         Again, do not be surprised if that level is over 0.1 volts.
 •       Adjust the bottom slug (primary) of T-501 for a peak
         reading on the VTVM
 •       Adjust the top slug (secondary) of T-502 for a peak
         reading on the VTVM
 •       Decrease the generator output and adjust the frequency
         to 455kc Note: The generator output should be decreased until the VTVM
         indicates approximately -3vdc.
 •       Select the 4kc filter then peak top and bottom of T-503 only

                                  AGC Alignment-

•        Verify the generator is still outputting 455.00kc. Set the FUNCTION
         switch to AGC and connect the VTVM between the AGC bus on TB-102 3
         & 4 located on the rear panel & ground.
•        Adjust the generator output for a reading of approximately -5vdc on the
         VTVM. Peak Z-503.

                               BFO Alignment-

 •       Verify that generator is still at 455.00kc
 •       Turn on the BFO and exactly zero beat it against the
         455.00 generator frequency.
 •       Loosen the bristo spline socket on the BFO shaft
 •       Verify that you still have exact zero beat.
 •       Set the BFO Pitch control to indicate exactly 0.
 •       Then, tighten the bristol socket on the non-mar
         clamp on the BFO shaft coupler
 •       The filters have been aligned to 455 kc.

(When a station broadcasting in AM is zero beat, the carrier will be in the
center of the filter selected).
• Re-install the IF chassis in the receiver.
IF deck tips                                      page 3

                     Setting the IF Gain Control for best performance

 The most common single item responsible for holding an R390A back is not lack
 of sensitivity. Rather it is internally generated IF deck noise. In an otherwise
 properly operating R390A, the cause of this excessive noise is IF gain control
 being set to high. Even the mfg spec of setting the IF deck gain such that -7vdc
 at the diode load when fed by 150uv @455kc into J-513 is far too hot.

 Here is a recently refined procedure to set the IF deck gain control. Anyone can
 perform the procedure whether they have access to a signal generator or not.
                                 Procedure to set R390A IF Gain-

 Once the receiver has been fully mechanically and electrically aligned, the final
 procedure to perform before buttoning it up is to set the IF gain control. Many
 otherwise very sensitive R390A's are thought not to be due to weak signals
 being covered by noise generated by excess IF deck gain.

 Allow the receiver to warm up for at least 1 hour then:

• Disconnect the antenna
•    Set receiver for 15.2 mHz
•    Set the FUNCTION control to MGC
•    Select the 4kc filter with the BANDWIDTH
•    Set RF GAIN control to 10 or maximum
•    Peak the ANTENNA TRIM for maximum noise as indicated on
     the LINE LEVEL meter
•    Set Line Meter switch to -10db scale
•    Set Line Gain control to full CW or 10.
•    Adjust IF gain control, R-519 to cause Line Level meter
     to indicate between -4 to -7 db.
•    Re-zero the carrier meter control, R-523
•    Set controls above for normal operation and reconnect


 This will yield the best compromise on all bands. I usually poll those bands
 which I normally spec out. Then, using an HP signal generator set for internal
 modulation of 800 hz @ 30%, massage the gain setting and even specific signal
 path tube selections for the best overall performance.

 Contribution by Chuck Rippel, WA4HHG
IF deck tips                                      page 4


                                 RF Deck Test-
I also encourage you to do a quick test that will verify the condition of your RF
deck and state of alignment. The procedure is as follows:

1-Disconnect the antenna
2-Set the Line Gain and Line Meter controls for a relative -5
       db indication on the Line Level meter.
3-Adjust the antenna trimer for a relative peak on the Line
       Level meter and note the position of the control.


An R390A with a properly operating RF deck is capable of peaking on its
own internal noise as indicated by the Line Level meter. Further, that peak
with no antenna connected should be coincident with the Ant Trim control
indicating 0.
Having the peak not occur at all indicates an RF deck failure or
poor/improper alignment. Additionally, improper alignment can also be
the case when the noise peak as indicated by the Line Level meter not
coincident with the 0 (+- .5) position on the Antenna Trim control. Chuck

IF deck tips                                      page 5

From: "Chuck Rippel" <crippel@...>
Date: Thu, 23 Oct 1997 09:01:39 +0500
Subject: [R-390] R390A AGC Problem

Now, I too am wrestling with an R390A AGC problem.

The basic symptom is: the receiver overloads for lack of AGC voltage. I develop
only about 2.2v v/s about 7.5v on a known working radio at the rear AGC
jumper for a 60db signal on the Carrier Meter. The time constants seem to be ok,
just does not produce enough voltage. I replaced the 82K, 1W R549 which has
drifted up to about 103K (seen it before) and had 82K 2W spares around.

Changing the IF deck out with a known working unit has no effect. The problem
stays with the radio.

I removed the RF deck and proved out the AGC bus checking both continuity
and to-ground resistances as compared with another deck. To ground resistance
was about 1.9M so its hard to believe that the RF deck is loading the bus down
yet, the AGC bus goes no where else.

Tonight, I plan to swap RF decks just to further isolate the problem. Assuming its
in the RF deck, my plan is to read the current at the AGC bus and compare it
with a known, good radio. Maybe someting is breaking down?? If it's in the RF
deck, the problem should be mentally easy to locate by just breaking the AGC
bus within the deck and watching for the voltage drop.

This is a I have not seen before and would appreciate some input if anyone has a
thought on it.
Date: Thu, 23 Oct 1997 23:10:02 +0500
From: "Chuck Rippel" <crippel@...>
Subject: [R-390] R390A AGC Problem Solved

Reference my earlier post about the AGC problem I was having with an R390A.
Essentially, there was not AGC as the control voltage measured at the AGC
jumber to ground was only -2v. It would rise when the RF deck was unplugged.

Tonight, after doing my usual routine on restoring an RF deck, I installed
another in the radio for test purposes. The test deck worked just fine. I made
some note on the operating parameters of the working deck with respect to
AGC. I left my millivolt meter which had been set up to read current across the
rear panel AGC bus. I had removed the jumper between terminals 3&4 on TB-
102 in configured the meter to read current between those two points. Since I
already knew the IF deck was good, any anomoly would be caused by the AGC
bus in the RF deck. The current across the AGC bus was typically 4ua with an off
air signal that nominally measured 70 on the carrier meter. Did not use a signal
generator because I felt that actual program material would reveal the resulting
distortion from a no AGC caused overload quicker.
IF deck tips                                      page 6

I reinstalled the defective deck and tested it. Same problem and the current
measured was >150ua. I then physically removed the deck from the main
chassis, connected it electrically and powered up the radio. Same input signal
except the AGC voltage was normal. What gives?

Looking across the bottom of the deck, I found that a .005 capacitor (no number
in my print) that was connected to pin 4 of V202 was pushing on C-273 causing
the hot end to ground (under a wiring harness so the potential problem was
hidden from sight/visual inspection), thus killing the AGC to V202 and V201.
Thus, the overload. I re-positioned the component and the AGC problem is

This failure looks like it has been that way since mfg. There were 3 RF deck
installation screws missing so I expect that someone had done some digging
looking for this problem. This radio is a Capeheart but in nearly new in
appearance and both electrical and mechanical operation. It now has a very hot
RF deck which easily peaks on its own noise (and that's not very much) when
the Antenna Trim control is rotated with no antennas attached.

The person that is getting this radio is getting an exceptional R390A. This radio is
no mongrel. thus far, all the Capheart modules match the main chassis.

R390A AGC Specs:

70 db as measured on the Carrier Meter results in:
(All measured at Terminals 3 and 4 of TB-102)

(-6) to (-7) Volts
4ua current between terminals 3&4, bus connector removed

Use an analogue VTVM as the dynamic nature of the changing voltage
would make measurement with a DVM very difficult.
Date: Tue, 28 Oct 1997 08:59:34 -0800
From: "James M. Toney, Jr." <tcltd@...>
Subject: Re: [R-390] (R-390) Why filters go bad - viz. bad caps

> ……what kills the mechanical filters in relation to (what) capacitors go bad.
> This probably relates to the compilation that I think was going on on the
> BA List a few weeks back, just before the establishment of the 390 mailing
> list I think - a record was being compiled of bad components……………

Brien, there is a capacitor in the input side of the mechical filter circuit, it is a 200V
cap (I think); the other side of the filters are grounded; if cap shorts filter killing
voltage goes thru filters to ground. Fix is to replace 200V cap with a 1KV and
isolate ground with a 1KV cap in series between filters and ground. Jim
IF deck tips                                      page 7

Date: Sun, 09 Nov 1997 21:28:49 -0600
From: Tom Norris <badger@...>
Subject: [R-390] Re: More on Electronic Assistance Corp./Hammarlund

At 10:14 PM 11/9/97 EST, you wrote:
>We have recently had a correspondent on the R-390 list server who *has*
>such a radio -- still with the ceramic filters! This may be one of the
>rarest R-390As around !!! He is correct in pointing out that the audio
>quality would be better than had the mechanical filters been installed.
>For the military, however, there was a practical degradation in intermod
>suppression in the harsh RF environment of a ship with multiple HF

Indeed, the audio is much better on AM with the ceramic filter deck! The AM
audio is "fuller" and hasn't the ringing of the "real" filters. I swept the deck at one
point, and the skirts are just a tad less steep. This deck is part of SN 127 EAC
contract 23137-PC-60. It is not a good a performer on crowded bands though, so
at the moment I have a 1954 Motorola deck installed......
From: John Kolb <jlkolb@...>
Date: Wed Dec 17, 1997 9:38 pm
Subject: Re: [R-390] More 4KC filter wierdness

<snip>... Let me describe Older Collins filters from a few I've opened. There are a
number ( 7 - 11 ) of metal alloy disks, typ 1/2" diameter, 1/8" thick in a row with
equal sized gaps, held together with a bonding wire welded to each disk.
attached to the two end disks is a fine wire, 1/2" long, about 36 gauge diameter.
A set of solonoid coils at each end surround these wires. The electrical signal is
applied to the coil at one end, which creates a magnetic field, causing the wire to
vibrate the first disk. The disks are like tuning forks, resonant at freqs near the IF
freq of the filter. If the applied signal is close in freq to the resonant freq of one of
the disks, it will be passed on to the end wire, which vibrates, inducing an
electrical signal in the other coil. If the freqs are too far from the resonant freq of
any of the disks they won't pass. There's also a small magnet at each end, parallel
to the transducer wire, creating a fixed magnetic bias on the transducer wire.

Most of the filters I've seen had custom rubber cushions supporting the
transducer assemblies at each end. Not much chance for change here. I've heard
that some of the older filters used a standard rubber grommet to hold the works
and that would fall apart with great age, causing the works to rattle around and
break the wires between the coil and terminals, if you were lucky; if you are
unlucky, the works would be bent beyond repair by the rattling around.

If the transducer wire were to break off, you get a very high insersion loss, but
that wouldn't recover. It may be that a speck of dust or flake of rosin flux got
into the filter and jammed between the coil bobbin and transducer wire. If so,
operation may cause vibration which would eventually change it's position.
IF deck tips                                      page 8

Collins filter data sheets may have limits on the applied signal voltage or DC
voltage or current through the filter (You generally should not let plate current
flow through the filter ) but they do not spec a maximum number of operating
hours or vibrations. Haven't heard of any filters dieing of old age other than the
ones noted above. I have opened and repaired a few filters where the coil wire
was broken between the coil and the terminal (wire fatigue??) or one case of no
solder on the terminal.
From: crippel@...
Date: Thu Dec 18, 1997 2:01 am
Subject: Re: [R-390] More 4KC filter wierdness

I have seen this happen before. Take the square filter cover off and wiggle the
wires going to the 4KC filter (its the one in the far rear). They are hard to solder
and I have seen them be soldered cold or even break loose.
From: "Chuck Rippel" <crippel@...>
Date: Sun Jan 25, 1998 1:51 pm
Subject: Re: [R-390] R-390a Repair

> Hello all, It is time to ask for help in repairing my first R-390A. I > have a
Stewart Warner >S/N 1831. On all bands 7Mhz and below, the sensitivity seems
to be down maybe 20DB or so. >The calibrator shows the same weakness >in
signal level. V202 tests fine, replaced anyway. >The 17Mhz osc signal is present at
V202 cathode. All voltages and resistance's at V202 check >fine. Z213-1 thru 3
tune and are peaking. I have removed the RF unit and inspected for >problems.
Wafer switches and contacts have ohmed out. Any ideas?

Check for a leaking/shorted capacitor inside the IF cans, Z-216-1, 2 or 3. Also,
one of those IF transformers could be bad.
From: Colin Thompson <burkec@...>
Date: Sat Jan 31, 1998 8:57 pm
Subject: [R-390] AGC settings

In the past there has been some talk about the appropriate AGC settings. I
would encourage all of you to try the Med or Slow settings, espcially for
stronger broadcast quality signals. The increase in fidelity is startling. For those
of use used to SSB and faster time constants, this may seem contrary. At one
point when considering modifying the AGC for better SSB, Chuck Rippel
reminded me that the R-390A is an AM reciever. The faster AGC mods would be
a compromise in the AM mode. The more I use these great recievers, the more I
come to know them and understand this. I have had some email dialog with
John Thorpe; Lowe HF225, HF150 and AOR7030 designer. All superior sounding
recievers. JT was famous for his slower AGC constants. He also restored a R-
390A to use as bench mark for designing the AOR7030. Slower AGC settings?
Food for thought.
IF deck tips                                      page 9

From: trinit69@... (Tom Marcotte N5OFF)
Date: Sun Feb 1, 1998 7:22 am
Subject: [R-390] 390A cap fail/fix

Another data point for the common failure list. I had to replace C-523 and R-551.

C-523 is a .005 uF bypass cap in the IF deck. It would short out at line voltages
over 90V. At that point, B+ was shorted through R-551 causing it to let the
smoke out of itself. I had the IF deck running external to this new rig, and thus
could witness the failure.

Replaced the cap and resistor.
Date: Sat, 27 Feb 1999 08:20:55 -0600
From: Dallas Lankford <dallas@bayou.com>
Subject: Q-spoiling resistors in the IF cans: purpose

I have also seen cut (but not cut off) Q-spoiling resistors in an R-390A IF deck and
all those IF transformers peaked to 455 kHz. Since this is clearly not how the IF
deck came off the production line, I did not mention it previously. The worst
case of this I have ever seen was with Q-spoiling resistors cut so that you could
not see the cuts without very close inspection (= magnification). I finally found
these "invisibly cut" Q-spoiling resistors because of intermittent jumps and drops
of signal levels of about 10 dB per the carrier meter. Heating and vibration
apparently caused enough movement of one of the cut resistor leads to open
and close the cut intermittently.

And yes, I will echo what Chuck said. An R-390A works much better with the Q-
spoiling resistors not cut , and the IF transformers stagger tuned (not all aligned
to 455 kHz as some people are going to do regardless of the correct way to do
it). I never cease to be amazed at some people thinking they know better than
the Collins engineers who designed, tested, redesigned, and retested the R-390A.

For those who think they know better, I would suggest a reeducation program,
beginning with reading "Final Engineering Report On Radio Receivers R-
389()/URR And R-390()/URR," September 15, 1953, A Publication Of The
Research And Development Laboratories, Collins Radio Company, Cedar
Rapids, Iowa (as required background reading for learning about the
R-390A), and Cost Reduction Program For Radio Receivers, R-390/391x/URR,
Final Progress Report," A Publication Of The Research And Development
Laboratories, Collins Radio Company, Cedar Rapids, Iowa (which is the story of
the development of the R-390A). Though stagger tuning is not specifically
mentioned in this report (to the best of my knowledge), we do find on page 15,"
New interstage coupling transformers were designed to give the required flat
top over a wide frequency range." What do you think this means? And your
first two guesses don't count.

                  Chuck Rippel wrote:
IF deck tips                                      page 10

> Just as an FYI... the stagger tuning of the T501/T502 accomodates
> the bandwidths of the 8 (really 11) and 16kc filters. When I perform
> that procedure, I select the 16kc filter then perform the stagger tune
> alignment on T501/T502.
> The tuning of T501 and T502 will appear somewhat more broad than
> you might otherwise expect due in part to the Q-spoiling resistors
> installed in the transformers. I have seen receivers where those have
> been incorrectly cut out and the transformers all tuned to 455 kc.
> Needless to say, the R-390A works much better if that is not done.
> > From TM 11-5820-358-35 (8 Dec 1961), pages 3 & 4, para 2(c) "Equipment
> > Modification Chart": "IF transformers T502 through T503 stagger-tuned at
the factory". Per the chart and its notes, this stagger-tuning applied as Mod
> > 1 on all Order No. 363-Phila-54 receivers, and also to Order No. 08719-Phila-
55 (serial numbers 600 and higher only, no Mod # indicated).
> > 73, Jerry W5KP
Date: Sat, 5 Jun 1999 12:35:57 EDT
From: JCStott@aol.com
Subject: Re: [R-390] Dirty but not so quick total setup

According to T.O. 31R1-2URR-452 (USAF Field and Depot Maintenance Manual),
page 4, Modification Table it states: "IF transformers T502 through T503 stagger
tuned at factory on Order No. 363-Phila-54, IF chassis MOD number
1....................." with a sub note stating: "This was also done to receivers on Order
No. 08719-Phila-55 with serial numbers 600 and higher." The T.O. that I have is
dated 8-12-1961 with change 12 dated 7-15-1975 I realize that this does not cover
everything but it is one piece of the information being discussed.
                         Z-503 AGC TRANSFORMER REPLACEMENT

Date: Sat, 27 Feb 1999 21:29:48 -0500
From: "Chuck Rippel" <crippel@erols.com>
Subject: [R-390] Re: Z-503 Replacement

As a suggestion to you and for the further edification of the list.

Z-503 is the AGC transformer. It can open but more often than not, the core
binds in the form. If it is forced during alignment, the core can break of the form
will come loose, rotate and break the feed wires. Before aligning it, put a >very,
very< small shot of WD-40 into the coil form and wait overnight. For some
reason, Z-503 cores can badly bind to the forms. I have found the WD-40 breaks
loose whatever the binding agent is allowing for easy alignment without
breakage. I have also yet to see any ill effects resulting from frugal introduction
of WD-40 into the coil.
IF deck tips                            page 11

If yours is open or the form is broken and not repairable, I think I have may
have a very Z-503 few >coils only< from American Trans-Coil and you can have
one for the asking. This assembly consists of the plastic (?) coil form with the coil
installed and two tinned wires only. I had a Z-503 open up and was able to
replace it without removing the entire coil assembly from the IF chassis (which is
difficult, just look underneath). I simply dissassembled
Z503 and replaced the open coil as follows:

Remove the 2 nuts holding the sheet metal cover from Z-503

Remove the 2 nuts holding the top insulator (with the tuning tool opening in it).

Carefully work the insulator off the coil while unsoldering the coil feed wires
that pass through it.

Closely cut or better, unsolder the 2 small wires which feed Z-503 and are
attached to the vertical feed wires in the coil form.

Carefully twist and pull on the Z-503 coil assembly lifiting it clear of the coil

At this point, its not a bad idea to check the internal, fixed value capacitor by
taking one lead loose and putting a megger on it. These have been known to
leak. Replace if required or simply re-attach the lead if it checks ok.

To install the new coil:

Put a small amount of epoxy glue on the bottom of the new coil form and install
it in the bottom insulator of the coil assembly.

Resolder the two Z-503 feed wires to the vertical wires in the coil form
reattaching them as closely to where the old ones were as possible.

Put a small amount of epoxy on the top of the coil form and reinstall the top
insulator being careful to make sure the vertical feed wires go through the top
grommets. Solder the vertical feed wires in the top grommets.

Reinstall the 2 nuts which secure the insulator to the coil base assy.

Reinstall the coil cover and hold down nuts.

Put a very small shot of WD-40 into the coil form to loosen the core and provide
for easy tuning.

Allow the glue to cure overnight.

After the glue is cured, realign the coil by injecting a 455.0 kc signal into J-513 on
the IF deck at about 300uv.... (of course, the rx is already warmed up and
IF deck tips                                      page 12

operating, the Function switch set to AGC and your VTVM attached to the rear
agc bus and ground) . Simply tune the transformer for a peak on the VTVM.

You are done.            Chuck Rippel, WA4HHG                   R390A List Co-Administrator
Date: Tue, 5 Oct 1999 09:58:02 -0700 (PDT)
From: John Kolb <jlkolb@cts.com>
Subject: Re: [R-390] Mech filter query

> I'm refurbing a spare R-390A IF unit - had a bad 8kc filter that was hacked
> out before I got it. Just so happens that the one and only spare part in my
> tons of junque box goodies is.... an 8kc filter !
> Anywho - does the in/out phasing of the filters matter?
> If the answer is yes, then I guess I get to stare at it some more. Also, if
> yes then I wud assume that the lead connections on the top and bottom of the
> filter are layed out physically to match the winding phasing.?.

Doesn't matter if the inputs are on the top or the bottom - the filter is
symmetrical. You would want the same arrangement as the other filters in that
IF section to have uniform wiring, and less chance of paths for RF to sneak
around the filter.

Before wiring the filter, it's a good idea to check the winding between the
terminals to make sure the coil is not open, and to check between the terminals
and case to make sure the filter is not shorted to gnd.

Don't forget that while in the IF section, there's a plate coupling cap which
should be replaced with a high quality unit. If it shorts, B+ goes through the
filters to ground destroying them.
Date: Tue, 05 Oct 1999 08:57 -0700 (PDT)
From: rlruszkowski@west.raytheon.com
Subject: Re:[R-390] Mech filter query

The two IF units I have are very different vintages - working one is w/o the
in/out trimmers, refurb is with trimmers. Plus there is a mix of filter lead
arrangements. Add to this my tired eyeballs and the tight spaces under there.

I do not remember phasing being a problem. The filters were replaced and best
fit used on the wiring. If your new unit has the trimmer caps then use then. They
do give a better impedance match, which is why they got added in later unit
coming off the assembly lines. Some filters have two terminals. Some filters have
three terminals. That third terminal was a ground lug. The mechanical
connection were suspect and a soldered ground wire was an improvement. If
your filter has a ground lug then solder a lead between it and the chassis. Some
units will have a bare wire between all four filters and then to a ground point.
IF deck tips                                      page 13

Date: Sat, 13 Nov 1999 10:57:57 -0600
From: "Dr. Gerald N. Johnson, P.E." <geraldj@ames.net>
Subject: Re: [R-390] I F Module

Fred, I think the AGC action IS being changed by a leaky AGC bypass or time
constant capacitor or a bad IF tube. Because looking at the AGC IF stage it has
only a resistor to ground from grid 1. The only way grid voltage changes is
because its being driven into grid current by an excessive signal. Pin2 (on the A)
was hooked to the developed AGC voltage when got large at -24 volts indicating
the signal level was extra large.

This lack of AGC control can also be caused by an AGC controlled stage with
excessive grid emission that makes the grid go positive and to have a grid
current that counteracts the applied AGC voltage.

Since the changes happen after the radio has been on a while, it looks more like
grid emission than a capacitor, though a capacitor's leakage can be temperature

So I'd check the AGC line at various places with a VTVM to see if was going
positive or zero when the radio was hot, and then look for the tube with grid
emission by trying to localize which one was back driving the AGC line, or else
I'd get out my grid emission tester and check the tubes that way (after I rebuilt
it). There usually are AGC isolation resistors for each stage to minimize feedback
through the AGC line and those will have high enough value (>100K) to let you
find the tube with the grid emission by finding the most positive grid.
Date: Sun, 26 Dec 1999 23:18:36 -0500
From: dave metz <metzd@cfw.com>
Subject: [R-390] Lankford AGC mods, ST. Julians finally finished

Having finally buttoned up a St Julians creek disaster after almost a year of
piddling away and some help from this group, I would like to say the hours
weren't worth it but the "experience" was everything! I really learned a lot.

To begin, as a matter or principle, I am not one who favors mods unless they get
me to the end of being able to use something better. Specifically, I like listening
to some of the military freq's such as 11.175 usb. Admittedly, I also have a couple
of R1051B's that will do the job quite nicely. However, given that this unit was
sort of an experiment to see if I could ever get it running, I felt it might be worth
the time to do a little experimenting. So I first disassembled the unit down to the
module level and removed the rf deck, took all the cans and racks out, removed
the front panel to refinish, and started by getting the modules except the rf deck
working in another 390A chassis. As far as cleaning, an aerosol degreaser was
used just prior to a hot water washer to clean up everything, especially the rf
deck. I covered the cans that couldn't be removed with duct tape. Then I final
rinsed with a gallon of distilled water and then put them in the attic during the
IF deck tips                            page 14

summer for a week to dry out. So, finally this fall, it was time to start the

Mostly, I wanted to make sure everything was working before I started "jacking"
with it. My first attempt was to do the IF mods on the unit per the suggestions of
the Electric radio series in #26 using 6jh6's and adding a diode and removing a
couple of resistors. My ear told me that this wasn't reallly satisfactory.
(Fortunately, I had not cut the swamping resistors in T501,2,3) So basically, I
removed/reversed that suggestion to the Lankford way. This is really simple,
remove one resistor add two capacitors and add two 1N4148 diodes. Dr
Langford suggested changing C551 to 1.22uf for the slow AGC and adding a
.47uf to lug 9 of S107 after lifting the white wire to ground for the medium agc. I
did this and found that I only used the medium position so I undid the 1.22 part
and only left the .47uf attached to lug 9 of the s107. I just used a dab of clear
silicone rubber to glue the cap to the inside of the front panel and the next day it
was firmly attached and yet still removeable. Bottom line: I can barely tell the
difference between the 1051B and the 390A. However, I did try the trick of
changing R541 from 270 ohms to 1000 suggested in the Electric radio series. I felt
that I just didn't have quite enough AGC and changing this resistor made a big
difference. My feeling was that because I have that "repaired" Z503 using a fixed
inductor and cap that maybe it isn't quite at resonance but this seemed to get
around the problem. I would sure hate to change Z503, boy would that be a job
even if one could find it! The last couple of things involved adding a 47pf cap in
parallel with the BFO injection cap per the Lankford way. And..... that ballast
tube bothered me. I just hate to spend $17 when there is less expensive ways that
aren't degrading. The first thought was to go 12BA6's and jumper the ballast
socket. I really didn't like the look of that hollow spot. So, for another twist on
the ballast tube alternative, I used a "pulled" 15DQ8 TV type tube and moved the
wires to # 3 and 4. This is so minor and given that I had to remove the BFO shaft
to change the injection cap anyway, it seemed a simple and cheap way to go. I
tried to use some 12v tubes but found that the low side voltage was a tad high.
The 15DQ8 put almost exactly 12.6 volts on the low side headed to the PTO and
BFO tubes. I know this sounds significant, but when all was said and done, I had
an IF deck that really handled the SSB and still made the BBC sound nice.

Then, I tried the RF deck mods suggested in the ER article. For whatever reason,
the bottom line here was that after I had good AGC with almost no distortion,
modifiying the rf deck to 6HA5's for mixers and changing the RF amp, created
unacceptable problems. First, I lost a significant amount of AGC. Secondly, I
couldn't open the rf gain completely without putting it
into oscillation or having almost no rf gain control with another type tube.
So, I reversed the entire rf deck mods and took it back to original. Perhaps there
is something else wrong in the rf deck or I missed the obvious when changing
the wiring for these mods but after reversal, it again ran beautifully.

In summary, I would highly recommend the IF deck mods suggested by Dallas
Lankford. They are simple and easily reversable. There are no holes or drills and
they allow a fantastic engineering marvel to copy SSB which was just coming on
line during early life and development. Primarily used for copying the fleet/unit
IF deck tips                                      page 15

broadcast in it's 8 and 16 mhz bandwidth, R390A didn't see a lot of SSB until the
end of it's life when the 1051 series came
to replace it in the Navy at least.

The final touch was putting on Tom Marcotte's replacement tag. When the choice
is no tag or a $9 almost authentic one, it isn't really a hard decision. I really take
my hat off to Tom for taking the time to develope them and to Dan Arney for
the covers. Those two guys deserve a lot of credit for the labor of love to make
available the replacement parts. Sorry this ran so long.
Date: Tue, 28 Dec 1999 12:36:10 -0700
From: Wally Gibbons <rockwall@sourceoneinternet.com>
Subject: [R-390] AGC woes!

Decided to use the holiday time for BA repair fun. My 390A is sick, overloading
on strong signals. I'm hoping someone has seen this and can say "replace this
capacitor, or tube"!

I'm listening to the audio, capacitor coupled off the diode load jumper and
feeding an external audio amp, by the way.

The diode load dc voltage will go to -40 volts on about any signal... AGC jumper
is at -12.5 on the local AM station I use as a test signal. I've watched the IF output
jack on a scope and the RF envelope doesn't appear to be clipping even though
the audio out on the diode load is.

By turning down the RF gain I can reduce the clipping but here's the strange
thing. With RF gain full up the audio clips on negative peaks. With it turned
down the clipping goes away for a while, then starts clipping on positive peaks.

As a frame of reference I looked at the diode load on my none-A 390 and it
hardly ever exceeds -8 volts, and doesn't clip on the local am signal either.
Sounds great.

Any clues? I'm going to jump in and search away, but hope someone as been
there and done that.
Date: Tue, 28 Dec 1999 14:48:23 -0600
From: "Dr. Gerald N. Johnson, P.E." <geraldj@ames.net>
Subject: Re: [R-390] AGC woes!

Controlled tubes with grid emission bucking AGC. Leaky AGC bypass
capacitors. The AGC circuit impedance is megohms so it takes very little leakage
in the AGC bypass capacitors (too low to measure with any ohmmeter) to kill
the AGC voltage. Trace the AGC voltage towards the tube grids with a VTVM.
Somewhere you will find it zero (leakage) or going positive (grid emission).
IF deck tips                                      page 16

Date: Thu, 30 Dec 1999 22:17:12 -0600
From: Nolan Lee <nlee@gs.verio.net>
Subject: Re: [R-390] AGC woes!

>Decided to use the holiday time for BA repair fun. My 390A is sick,
>overloading on strong signals. I'm hoping someone has seen this and can
>say "replace this capacitor, or tube"!

There's a good chance it's a leaky cap in the AGC circuit in the IF deck. It's little
recurring problems like this that are a pain to track down that lead to my policy
of simply replacing all of the under chassis paper caps in the receiver.
ESPECIALLY, the IF deck. It'll cost you about eight or ten dollars in parts and a
few hours of your time to go thru the IF deck and recap it. It's time and money
well spent in the long run. I'll post my R390A capacitor list to the list in my next
Date: Mon, 10 Jan 2000 08:35:15 -0600
From: pbigelow@us.ibm.com
Subject: [R-390] Distortion / IF alignment

After checking/replacing capacitors and resistors, cleaning, and aligning (again)
my R-390a was STILL having distortion problems with strong signals. Stagger
tuning or peaking the IF at 455 did not help. Throwing my own beliefs about the
problem out the window (RF overload on the front end), I decided to pursue the
problem as an AGC problem.

These strong stations, S9+30db or S9+50db (on AM BCB band) distort some on
speech but distort rather badly on music. One station plays a lot of R&B with lots
of bass notes and is particularly prone to distortion, but is "weaker" from a
STRONG signal perspective -- S9+30db, or thereabouts.

Using that station as a guide, I measured the AGC - about -10.7v - not bad right?
Other, stronger, stations measured -12.1v. Well, assuming that for whatever
reason the AGC voltage was not enough, this morning
(very quickly) I did the following:

1. Using the .1 and 1kc filters CAREFULLY turned the R&B station for max
2. Monitored the station through headphones
3. Set the AGC for fast
4. Placed the VM on the AGC line
5. Slowly adjusted the T501,T502,T503, and Z503 for maximum AGC voltage /
lowest distortion

Guess what? The distortion was reduced dramatically to virtually non-existent
and the signal strength of the station on the R-390a was still at 100db and the
IF deck tips                                      page 17

AGC voltage was increased to about -11.6v. I used Chuck Rippel's IF gain
method and ensured that the gain level was kept within his recommendations.

What does this tell me?

1. My previous alignments were incorrect every time?
2. The peak frequency of the coils is not 455kc?
3. Stations overmodulate causing a need to "touch up" the alignment based n
hearing / distortion meter?
4. I am masking some other problem?

To me this seems a bit nuts but is alignment based on maximum AGC voltage a
valid alignment method? Or, would the idea be:

First, use a stagger tuned or 455kc peak IF alignment method
Second, touch up by maximizing the AGC with a STRONG station
This will be investigated further but I would like comments.
Date: Mon, 10 Jan 2000 10:39:04 -0600
From: "Dr. Gerald N. Johnson, P.E." <geraldj@ames.net>
Subject: Re: [R-390] Distortion / IF alignment

Aligning the AGC stages for maximum AGC voltage is appropriate. Aligning the
variable bandwidth stages for maximum AGC may easily destroy the predicted
Date: Sat, 22 Jan 2000 10:23:08 EST
From: PABigelow@aol.com
Subject: [R-390] E208-E211 Test Points

Thanks Nolan, Walter, and everyone for suggestions and help. What brings
about the discussion for the DVM vs VTVM are my measurements at E208-E211
on the RF deck. The Radio Shack DVM measures wildly different voltages at
these test points, but something else is happening... As reference: Using the CAL
signal and adjusting RF GAIN the AGC point on back panel measures at -5.0v

*E208 -2.041v              E209 -4.60v                *E210 +.28 mv              *E211 -1v

These test points should measure about the same. Is that correct?

*In the case of E208,E210, and E211 touching the probe to the test point causes
the carrier level to change noticeably. So, either capacitance or load of the DVM
is affecting the AGC voltage. Correct? The measured resistance from ground to
these points are (tubes in place, power off):

E208 .505 M                E209 1.416 M               E210 1.406 M               E211 .840 M

Ideas or suggestions? Turning off the auto range feature on the DVM does not
help. Maybe the VTVM is a necessity? Probes a problem perhaps?
IF deck tips                                      page 18

Date: Sat, 22 Jan 2000 11:04:41 -0500
From: "Walter Wilson" <wewilson@knology.net>
Subject: Re: [R-390] E208-E211 Test Points

The resistance measurements with the function switch in AGC and the radio
turned off should be pretty close to:

E208 1M                    E209 1.6M                  E210 1.6M                 E211 1M

(see page 116 of TM 11-856A)

You listed: E208 .505 M             > E209 1.416 M          > E210 1.406 M > E211 .840 M

You should see much closer to 1M from E208 to ground. You should easure
about 500K from the AGC test point to ground (220K + 180K + 100K), and 500K
(470K + 22K) from the AGC test point to E208. Look at Figure 104 on page 183
in the TM 11-856A.
Sat, 22 Jan 2000 11:31:27 -0500
From: "Walter Wilson" <wewilson@knology.net>
Subject: Re: [R-390] E208-E211 Test Points

I said in an earlier post that E208 should be closer to 1M. But I see a discrepancy
between the AGC schematic (figure 104, page 183) and the schematic of the RF
amplifier. One of these is in error. These schematics show test point E208 on
different sides of the 470K resistor feeding AGC voltage to the grid of V201. The
final answer is to measure the resistance between pin 1 of V201 and ground.
That should be close to 1M.

I hope the updated manual folks are working on correct this error.
Date: Sat, 22 Jan 2000 11:31:37 EST
From: PABigelow@aol.com
Subject: Re: [R-390] E208-E211 Test Points

Allright, with the receiver not plugged in AND the switch to the AGC position --
measurements are: E208 .505 M, E209 1.419 M, E210 1.409 M, E211 .843 M

Little change from the OFF position.

AGC (on back panel) to GND: .377 M
AGC to E208 .245 M

I have the TM 11-5820-358-35 copy from Fair Radio

Nevertheless, the AGC to GND result should have me check R545, R546, R547 or
maybe a short in C547,or C548?
IF deck tips                                      page 19

Date: Sat, 22 Jan 2000 11:36:51 EST
From: PABigelow@aol.com
Subject: Re: [R-390] E208-E211 Test Points

Pin 1 on V201 measures .993 M so that would appear OK.
Date: Sat, 22 Jan 2000 11:15:53 -0600
From: "Dr. Gerald N. Johnson, P.E." <geraldj@ames.net>
Subject: Re: [R-390] E208-E211 Test Points

First try putting a megohm in series with the test probe at each test point to
isolate the DVM. The DVM may be affecting AGC voltage.

There are series isolation resistors in the AGC circuit. Having lower voltages at
different test points comes from leaky AGC capacitors or tubes with grid
emission. Or a voltage divider to reduce the application of AGC to the RF stage. I
don't have the circuit in front of me to see if there's any way that the DVM
should otherwise affect those voltages. A grid voltage test point with a positive
bias is a sure sign of grid emission, not capacitive leakage.

You might pull the RF and IF tubes and apply DC from a 9 volt battery (positive
to ground) to the AGC line and see what the voltage distribution sans tubes is.
Won't need power for that.
Date: Sat, 22 Jan 2000 14:37:02 -0500
From: "Walter Wilson" <wewilson@knology.net>
Subject: Re: [R-390] E208-E211 Test Points

Since pin1 to ground measures almost 1M, and E208 to ground measures much
less, it seems to confirm that placement of E208 is correct in the RF deck
schematic and incorrect in the AGC schematic (figure 104 of TM 11-856A). All
would seem OK since pin1 of V201 to ground measures close to 1M.

> AGC (on back panel) to GND: .377 M I've done some of the Dallas Lankford
SSB mods, so my readings are irrelevant for comparison AGC to E208 .245 M
mine was .240M

I couldn't resolve the measurements from AGC to E208 with the AGC schematic.
But I found it has ANOTHER error. It shows R201 as 22K, but the detailed
schematic confirms this resistor is 270K. So all is well once again.

> Nevertheless, the AGC to GND result should have me check R545, R546, R547
or maybe a short in C547,or C548?

Agreed that AGC to ground should measure 500K; that is IF you have not done
any SSB mods in this area. Just to rule out C551, measure from the AGC test
point to ground while swapping the AGC switch from fast to medium. Should
IF deck tips                                      page 20

be no change unless C551 is leaking badly. If no mods have been done, this area
would be worth checking for bad caps.

<snipped from another message:>
> The measurements I made with the AGC test point had the jumper in place for
NORMAL not Diversity.
> I'm thinking that with the measurements I should remove the jumper.

Leave the jumper in place for NORMAL.

I'd keep looking at the tubes, based on the readings you've quoted so far. Even
with the AGC to ground resistance reading, that does not explain why you're
not getting the AGC voltage to the grids of the RF amp and mixers. Your
resistance measurements look OK on the RF deck to the AGC jumper. So any
voltage more positive that the applied AGC voltage leads me to still want to try
swaping tubes around. For a test, you could take your best mixer tube which
appears to be at V202, and swap it with the tube in V203 (or V204). If the -4.5
volts grid bias moves with the tube, you've found your problem.
Date: Sun, 23 Jan 2000 15:57:38 -0600
From: "Dr. Gerald N. Johnson, P.E." <geraldj@ames.net>
Subject: Re: [R-390] R-390a distortion and measurements.

Last night I pulled the paper capacitors from a Heathkit audio VTVM to rebuild
it. I'd already bought new capacitors, but after it was working, I checked them.
None showed up lower than 20 Megohms on my DVM. When I put them on my
capacitor tester none showed up passing the leakage test and most showed a
significant power factor 5 to 10%. When I gave them my tough leakage test in its
least sensitive mode, the best leaked 1 microamp at 450 volts, the worst leaked
80 microamps at 200 volts. That last one was a 2 mf molded (not black beauty)
that had never had more than a couple volts applied all its life. So its leakage was
just the result of age.

Have you REPLACED the AGC and other black beauties yet, or are you wasting
time trying to prove they don't need replacement? That means in the RF section
too. Poor AGC action says AGC bypass capacitors or tubes or AGC IF alignment
and gain.
Date: Wed, 02 Feb 2000 17:26:57 -0600
From: "Dr. Gerald N. Johnson, P.E." <geraldj@ames.net>
Subject: Re: [R-390] VTVM and E208, E209, E210, E211

Paul, your Senior VoltOhmyst has a megohm or so of resistor in the tip of the
probe? Then it should look like about 11 megohms input Z?

Then if you find a lower voltage at the test point out front that means either the
VTVM is loading the circuit, e.g. at the point where the VTVM reads -2.5 volts
the series Z to that point in the receiver is 11 megohms (truly bad solder
IF deck tips                                      page 21

connection or resistor), or leaky AGC bypass capacitors are loading down the
voltage, or there's a tube or two with a lot of grid emission producing a positive
bias to counter the negative bias from the AGC detector.

As a test, find a matched set of 1 megohm resistors and solder one to each test
point and see if the VTVM still changes the signal level meter. It shouldn't.

This is solvable.

Another test. Turn the radio off and let the tubes cool, or pull them. Apply -9
volts from a transistor radio battery (positive to ground) to the AGC jumper on
the back panel. See if the voltage is the same at the test points. If it isn't then
there's R or C problems. If it is the same with the tubes missing or cold, there's a
tube with bad grid emission. I've run into that at about 4 year intervals on my
75S3B so I KNOW it happens. Watching the voltage change as you plug the tubes
back one at a time (at several minute intervals) will dramatically SHOW which
tubes are contributing grid current from grid emission.                          73, Jerry, K0CQ
Date: Wed, 02 Feb 2000 17:33:29 -0600
From: "Dr. Gerald N. Johnson, P.E." <geraldj@ames.net>
Subject: Re: [R-390] VTVM and E208, E209, E210, E211

Hmmm... could Paul have an RF stage oscillating at a couple hundred MHz?
Date: Wed, 02 Feb 2000 21:57:23 -0600
From: "Dr. Gerald N. Johnson, P.E." <geraldj@ames.net>
Subject: Re: [R-390] VTVM and E208, E209, E210, E211

And if they did, it would drive the grid circuit negative, NOT POSITIVE! The only
things that can be failing or tubes with grid emission, leaky AGC bypass
capacitors or open series resistors. I stick by my prescribed tests with the 9 volt
battery, then if that proves the resistors and capacitors are good it has to be
tubes with grid emission which will show up by heating up one tube at a time.
Date: Thu, 03 Feb 2000 02:18:03 -0600
From: "Dr. Gerald N. Johnson, P.E." <geraldj@ames.net>
Subject: Re: [R-390] VTVM and E208, E209, E210, E211

Even if a generator was driving watts into the RF stage that wouldn't make the
DC grid voltage go positive! It would make it go negative. The original and
persistent complaint is distortion on strong signals. And the VTVM tests show
reduced AGC on the RF deck compared to the AGC voltage on the AGC jumper.
And the VTVM tests indicate putting the probe on the test points changes the
signal level meter, e.g. the AGC voltage. That shouldn't be if those test points are
DC and the VTVM truly is 12.5 Megohm input Z. Unless there's a near open
series impedance in the AGC, or a lot of leakage in AGC bypasses, or a tube or
more than one tube with grid emission. Its the grid emission that can drive the
AGC voltage towards positive, e.g. less negative. At least that's what it does to
my 75S3B...        73, Jerry, K0CQ
IF deck tips                                      page 22

Date: Tue, 15 Feb 2000 11:05:19 -0600
From: Nolan Lee <nlee@gs.verio.net>
Subject: [R-390] 390A Bandwidth Switch Replacement ..

>Hi I am still looking for the section of the bandwidth switch that comes
>throught the front of the IF deck bushing...

I can't believe that no one has replied to you about this. Rather than of scrapping
an IF deck for the part, fix it. It's easy enough. I've explained two different
methods below. It's kind of like the "good news, bad news" thing. One takes
some work. The other is easy. The hard one is first. <grin> :-)

First, I've never seen one that the shaft was broken off on. I've seen a couple
where one leg of the copper detent spring had cracked and allowed the detent
ball to fall out. I've replace several of these springs and detent balls.

If you're handy with tools, you should be able to make a replacement shaft easy
enough though. The groove looks to be about .025 wide. You can determine the
depth from your old shaft. You might have to juggle the width and depth of the
groove depending on the dimensions of the external snap ring used as a
replacement for the original C clip. I just dug a couple of the detent assemblies
out and measured the length of the part of the shaft that you're missing. From
the face of the threaded panel bushing to the end of the shaft extends .897 on one
and .901 on the other.

>the IF deck I have is 2 pieces that are joined with a shaft coupler...

Correct. The short shaft that extends thru the detent portion is brass and the rear
section that extends thru the wafers is aluminum.

>the front section on my deck has been cut at the "C" ring groove, and I need the
part that connects to the Knob shaft coupling and goes through the Deck
bushing and connects to the switch shaft...

It looks easy enough to make a replacement if you're handy with hand tools. All
you'd really need is a a piece of 1/4 brass or aluminum (brass preferred) shaft,
an external snap ring and snap ring pliers, a hacksaw, a file, a small sharp cold
chisel, and a 4 oz or so ballpeen hammer. The tedious part will be filing the flats
on the shaft for the detent plate and spring. The only tricky part will be restaking
the detent spring on the new shaft. You'll want that chisel sharp when you do.

Cutting the groove is easy enough. Chuck the shaft in an drill press or an
electric, verify that the directions it's spinning is into the teeth and put the hack
saw to it. If you have to, you can vary the width of the groove. A well worn fine
tooth (32T) blade will cut a narrower groove than a new coarse (18T) blade. I've
modified blade thicknesses in the past for cutting soft materials like brass by
thinning a section of the blade with either a grinder or a sanding drum.
IF deck tips                                    page 23

It looks like the only measurement that you'd want to be careful with would the
distance between the groove and the end of the two flats where the detent stop
plate sits. Cut the groove first than file the flats.

The "easy" option would be to cut up and modify the detent part of an old rotary
switch. Looking at the detent assembly, it's got a total of twelve detent positions,
only six of which are used. That would mean that each of the detent positions are
30 degrees apart for a total of 150 degrees of shaft rotation for the six positions.

If you've got an old multi sectional wafer switch with 30 degree detent spacing
(pretty common) and a shaft that extents at least .9 inches past the panel bushing
you should be able modify and use it. Or you might just want to use just the
shaft out of it and modify it to fit your existing panel bushing.

I just took a look at some switches I have and it appears that the shaft design and
detent mechanism is a common design used on a lot of rotary switches. It looks
like plated steel and aluminum are a lot more common that the stainless steel
used in the R390A though. Thanks to the coupling that it uses to attach to the
rear shaft, the relationship of the flats on the shaft to the detents is unimportant.
If you use a switch that's already setup for less than six positions, opening up the
stops is pretty easy. Adding a stop if you only have something like a seven
position switch is more work. ;-)

If you do cut down a switch, cut the back end of the shaft about 5/16 of an inch
or so longer than the original and remove that amount from the second long
shaft where it's tapered. It'll clamp a lot nicer in the coupling and is more reliable.

If you've got a decently stocked junk box, you have the parts you need to fix
your radio.

>I have seen mentions of this part, but I am not sure of the exact
>name for this piece... Is it normal for the shaft to be 2 sections???

I'd guess that "bandwidth switch detent assembly" would be a good description.

>someone mentioned that I would have to remove all the switch wafers
>to perform the repair, but it is not the case... the front section
>with the detent is easily removed from the EAC deck, and the shaft
>can be removed entirely through the rear opening in the deck...

Yep. It's a handy feature. Sliding the shaft out makes it a hell of a lot easier to
replace some of the capacitors in the IF deck. Ditto if you need to change one of
the mechanical filters. I wish that the rear shaft was a little longer though. I don't
care for the tapered end where the shaft coupling goes. ;-)
IF deck tips                                      page 24

Date: Thu, 16 Mar 2000 17:38 -0800 (PST)
From: rlruszkowski@west.raytheon.com
Subject: [R-390] BFO Adjustment

Can you find WWV at 5.000 10.000 or 20.000 MHz?

Set the dial to 10.000 in AGC or MGC center WWV as best you can down to the
100 hertz crystal filter in the IF deck. Get out your trusty spline tool and loosen
the BFO clamp on the BFO
extension shaft. The BFO is an inductor and has some good 3 turn range to it.
Grab the shaft with a pair of pliers and rotate it to zero beat on WWV.
Hold the knob on the front panel at zero. Retighten the clamp. Repeat this
process until you get the knob on zero, WWV center in the filter pass and the
BFO zero beated. This will get your BFO within a 100 hertz of 455KC. Switch the
receiver to cal. Adjust the cal trim on the back panel to zero the crystal calibrator
to zero beat. Try to do this at 20.000 Mhz for better
adjustment than at 5 or 10. That what you can get. This will get your dial, PTO,
BFO, and crystal calibrator in alignment. Go down 1 Mhz and roll the PTO to
+000 this will give you an Idea of what you PTO band spread is. (good is under
1KZ. 1-3 ok more than 3 is a candidate for alignment.) You should be able to
predict where CHU (7335) will zero beat on your dial. Knowing your PTO
spread and zeroing against your aligned cal tone at 7.300 you should be able to
hit CHU right on at 7.335. The BFO should zero and give all your stations and cal
tones very nice zeros and sweep on both sides of zero.

There is also a BFO neutralize cap on the side of the receiver. It has some range
to it. Hang a volt meter on the diode load. Tune to dead air space. Turn the BFO
on. Adjust the trimmer cap to find a range of minimum output on the meter. Set
the cap to mid range of the minimum. This just helps to reduce the BFO injection

To tune single side band, Calibrate your receiver to a Cal tone. Roll the receiver
down 2Khz. Turn the BFO to the plus side to zero the tone. Mark that spot on
the front panel. For micro dial guys try a value of 16. Start hunting your SSB with
that setting. Once you get one you can get a better offset.

Chris, Your receivers prior owner may have off set the BFO knob. Cal tone zero
may be at -2 and SSB be at 0. try this once before you make any adjustments.
IF deck tips                                      page 25

Date: Mon, 10 Apr 2000 19:15:23 -0400
From: "Dan Martin" <dmartin@visuallink.com>
Subject: Re: [R-390] AGC Voltage

I seem to recall Chuck keeps some helpful AGC troubleshooting experiences on
his web site. Suggest you try http://www.avslvb.com/R390A/
html/Commonfail.htm and see what you can find.

There is a pin on the big jack on the IF deck that is the IF AGC line. It should test
to infinity with an ohmmeter. Anything less could suggest a leaky cap or
something. I've found it to be a good quick check of the "height" above ground
for the IF AGC line. You mention "diode load" in your checks below. Perhaps
you mean the AGC jumper on the back panel. I think somewhere between -8 to
-11 V or so is typical of my '67 EAC with a strong signal. The TM may speak to
this but I don't have it near me.
Date: Wed, 12 Apr 2000 15:42 -0700 (PDT)
From: rlruszkowski@west.raytheon.com
Subject: Re:[R-390] Torque on the BFO

Sun, You have a problem. Yes these things can feel the way you describe. It can
be cured. Are you up to open heart surgery on a baby? Proceed at your own
risk. Ignore all warning labels. Unsolder the three leads across the front and haul
that BFO can out of the chassis. Open it up and be carefully. Clean the front shaft
bearing up. Check the slug alignment down through the coil for drag. re lube,
reassemble and enjoy. They should run pretty smooth. There is a fair amount of
drag. You should be able turn the shaft with your fingers. It should feel about
the same as the ant. trim knob. Whole assemblies dragging from the front panel
is mostly alignment of the shafts through the front panel and IF deck bushings.
Bad micro dials will also add drag.
Date: Tue, 18 Apr 2000 08:24:17 -0400
From: "Randall C. Stout" <rcs1@sprintmail.com>
Subject: [R-390] 1ST IF ?

I am plowing through my Collins blue striper and made my first run through on
alignment last night. I had one development that leaves me puzzled.

While aligning the 1st variable IF stage, using the freq and hookup that Chuck
recomends, I found that I had to screw the slugs almost all the way out(the
adjuster sticking way up out of the rack.) The caps, esp. on the rearemost can,
took a lot of adjusting too. I went over it 4-5 times, and kept getting the same
result. I thought perhaps my cam was out of time, or not lifting the rack enough,
but I checked it against another rig, and the rack lifts exactly the same amount,
but the slugs are probably 10 mm further out of the coils. The second variable IF
slugs are at a more typical mid position.
IF deck tips                                      page 26

This rig has a replacement set of cans for this rack. They aren't marked on the
top as most I have seen, but have Z213 on the side of the can. I think they might
be the type used on Teledynes. The only marking I could see other than the Z213
was TSC in a circle inked on the top.

Does this ring a bell with anyone? The radio had been very deaf below 2khz,
only picking up the loudest broadcast stations, but now it is pretty sharp, with
stations all over the band. I not trying to argue with success, but I wonder why
these slugs are so far out.

Are the three coils different from each other? The three cans just say Z213, not
Z213-1 ,Z213-2, etc. The Collins cans have that kind of marking on them.
Date: Tue, 18 Apr 2000 08:29:19 -0400
From: "Randall C. Stout" <rcs1@sprintmail.com>
Subject: [R-390] T503 ?

While going through the blue striper Collins, I also noticed that T503 was acting
odd. When I tried to adjust the coils, it acted like there was an intemittant open in
the can, where the diode reading would drop way down, then spring back up,
even with just the slightest twisting of the adjusters. I thought that this
adjustment usually showed a very broad peak, not very sensitive. The rig seems
to be working however, and I don't hear anything different in the way the filters
sound. What happens to the sound when T503 goes bad? Thanks - puzzling
through the Collins
Date: Tue, 18 Apr 2000 10:07:16 -0400
From: "Ronald Reams" <wa4mjf@worldnet.att.net>
Subject: Re: [R-390] Questions

As for alignment, you would need:

Signal Generator (AN/URM-25 or similar)                        Multimeter (TS-505/U or similar)
Audio Oscillator (TS-382/U or similar)                         Electronic Voltmeter (ME-30/U
or similar)
Oscilloscope (OS-8/U or similar)                      Output Meter (TS-585/U or similar)
Date: Tue, 18 Apr 2000 07:59 -0700 (PDT)
From: rlruszkowski@west.raytheon.com
Subject: Re:[R-390] T503 ?

I just hit this last week end in T502. Off with the cover and resolder all the joints
in there. Check the ones on the bottom side also. If just bumping things gets you
a jump, go solder.
IF deck tips                                      page 27

Date: Tue, 25 Apr 2000 13:24:55 -0500
From: "Scott, Barry (Clyde B)" <cbscott@ingr.com>
Subject: [R-390] Crystal Oscillator questions

Okay, time for one easy question and one bone-headed one.

Easy: Can someone tell me where to look on the schematic for L402? It is a
choke mounted on TB402 in the crystal oscillator deck. I can find L401, but not

Bone-Headeded: I hooked up the crystal oscillator deck last night and did some
preliminary tests. Hooking the output to the frequency counter showed each
position to be within 200 - 300cps which I assume is okay. However, looking at
the output on the scope, I have a VERY weak signal, along the lines of 50mV or
less (much less on the higher frequencies). The tube checked good. Also, I
noticed that I have only 45mV on the grid (E401).

I ASSUME the reason I get such a small grid voltage is there is very little grid
current. Furthermore, I ASSUME this is a result of little (or no) plate current. If
I'm on the right track, I should be able to measure the drop across R406 or R407
to determine this. Also, do I need to terminate J415 into a proper Z to see the
output voltage correctly?
Date: Wed, 26 Apr 2000 08:36 -0700 (PDT)
From: rlruszkowski@west.raytheon.com
Subject: Re:[R-390] Crystal Oscillator Problem(s)

>............An additional note, while looking at the control grid voltage on the
>scope, if I go to 50mV/Div, AC mode, the signal bounces all over the place. It
appears to have a very small rf signal (5 or 10mV), but it moves at random up
>and down on the scope, +/- 50mV or more. I tried two tubes with no change.
>Any ideas at all?? Thanks, Barry

Barry, You are going to stuff that signal into a mixer tube that has less that 20uv
of signal. 20mv of mixer is more than OK. Change in output level on the same
crystal is no problem. Your in a test setup and stray cap on the bench is getting
you. Adjust the deck can coil and the band cap for best output on the weakest
crystal frequency. Then trim all the other caps for their band. If you have a real
weak crystal, swap a couple crystals in their sockets and look at them on the
scope. If the weakness stays with the socket and band go looking for a cap
problem. If the weakness moves with the crystal find a replacement crystal. You
can take every thing out of the chassis and disassemble those little caps and clean
them up. We use to order the RF deck cans and use the trimmer parts out of
them for the top adjuster and the retainer clip. The range value is amount of
silver area on the other section of the cap. You can clean these all up. Some times,
some thing conductive gets smeared into the cap. This changes its value. A good
cleaning fixes that. I hated to do a major clean job on a crystal osc. chassis. It took
a whole damn shift. But maybe once again after this many years would be in
IF deck tips                                      page 28

order. If you have a blue striper I would take the time. It would be a once in
your life time event. If you booboo you can ask fair radio for a RF can to get
parts. get the DeOxit to clean up the little silver retainers on the bottom side.
Roger KC6TRU
Date: Fri, 28 Apr 2000 22:20:11 -0400
From: "Patrick Rady" <haenck@mediaone.net>
Subject: [R-390] Filter *Cap* Confusion

Many thanks to those who responded to my message about identifying filters. I
am convinced now that I have the right replacement and now know where it
needs to go. I really appreciate your expertise here.

Now, at the risk of opening a can of worms... I have another question. I tried
searching the archives for the answer but to no avail... In another functioning IF
deck of my acquaintance I was dismayed to find a lowly disk capacitor sitting
atop one the filters instead of the red Mica capacitor that looks not unlike a
domino. Worse, the solder joint was history and the lead slides up and down on
the wire it is supposedly connected to. Not good. Before I whip out the
soldering iron... is a Ceramic Disk cap a worthy replacement for the red
rectangular Micas [?] that I usually see in this location? If not, what is?
Date: Fri, 28 Apr 2000 23:02:11 -0400 (EDT)
From: Norman Ryan <nryan@duke.edu>
Subject: Re: [R-390] Filter *Cap* Confusion

> ... is a Ceramic Disk cap a worthy replacement for the red rectangular Micas

A dipped silver mica is the way to go. Get one with a 500VDC rating. Are you
replacing the two B+ caps also? C549 and C553. Failure of the latter is death to
mechanical filters. I go overboard with orange drops here-- 0.01 mF @600VDC.
Date: Fri, 28 Apr 2000 21:18:26 -0500
From: "Dr. Gerald N. Johnson" <geraldj@ames.net>
Subject: Re: [R-390] Filter *Cap* Confusion

For that tuning application an NPO ceramic might be adequate though the silver
mica would be a bit more stable. Any ceramic other than NPO or Nxxx
temperature compensating will not stay within any reasonable range of the
value required to tune the filter. A modern dipped silver mica would be the
optimum replacement in a fixed capacitor, though a gang of ceramic trimmers to
tweak the filter resonance might improve the flatness of some filter passbands. I
learned that the hard way once trying to build a miniature tube IF strip and
where I used some small dogbone shaped tuning capacitors. I found they
wouldn't stay resonated because the tube heat change the capacitance more than
25%. I put one of the offending capacitors on a bridge and heating it up to
soldering temperature the C went from 180 down to about 40 pf. Far more
variation than tolerable for a tuning capacitor.
IF deck tips                                      page 29

Date: Wed, 31 May 2000 09:18:00 -0500
From: "Scott, Barry (Clyde B)" <cbscott@ingr.com>
Subject: [R-390] Z201 problem

I have been having problems with the 0.5-1mc band. I noticed I could not get a
peak with the slug or the cap on Z201-2. I pulled it out and checked continuity
across the coil - infinity. Opened the case and saw the problem - - a broken wire.
Not just any old broken wire, but the wire from the top of the coil to the
capacitor clip.

At some point, I remember snapping the clip off one of the caps to check
something. It turns out it was on this coil. When I pushed the clip back, there
wasn't enough slack in the (Litz?) wire to the clip and it broke. The wire is so
small that I didn't even notice it.

To make it worse, this end of the coil is the part that's wound first meaning the
lead goes underneath the rest of the coil. If it were the other end, I might could
unwind one turn and have something to work with. As it is, my only solution is
to attempt to splice it. I tried to position the wires just so they would touch so I
could determine if it would align properly, but this turned out to be like nailing
Jello to a tree - I couldn't do it.

Is this tiny, stranded, coated wire solderable? It is going to be a real pain to do
this, but I can't think of any other alternative.

I thought I would mention this as a warning to others. Be careful if you decide to
pop the top off these caps. If there isn't enough slack in the lead wire, you could
break it as I did.

Other than "Keep your hands out of that radio before you completely destroy
it!", any other suggestions?

Date: Wed, 31 May 2000 10:22:03 -0500
From: "Dr. Gerald N. Johnson" <geraldj@ames.net>
Subject: Re: [R-390] Z201 problem

Since each strand of litz wire is enameled separately and those sub hair diameter
strands are fragile its a pain to strip. Either a chemical enamel stripper like Strip-
eze or an open flame are effective. If all you have exposed is the broken end and
can't get some added wire to get more solder area, any patch is going to be very

I've not tried it but IF you can get contact by mechanical positioning, maybe
some conductive epoxy may make a repair. Its good for tiny microwave parts
and might make a stronger connection because the epoxy should stick to
insulation as well as bare copper.
IF deck tips                                      page 30

Date: Wed, 31 May 2000 14:40:38 -0500
From: Roy Morgan <roy.morgan@nist.gov>
Subject: Re: [R-390] Z201 problem

... When I pushed the clip back, there wasn't enough slack in the (Litz?) wire to
the clip and it broke...............

Litz wire is very delicate. You can put the end in a flame from a candle and it
may burn off the insulation. You should get EVERY of the (probably) 7 strands
connected for best results. I use a very sharp scalpel and work very carefully to
mechanically strip the varnish coating from the strands. You have to support the
wire so you don't break it again. Solder a piece of solid wire to the terminal long
enough to go over near the free end of the litz wire where you solder the two
together. And leave a bit of slack in the litz so it won't get stressed and break

"Litz" is from the German word litzendraft which means drawn very lightly, or
drawn out to be very light. Most litz wire is seven strands of no. 40 wire. The
largest Litz wire I ever saw was in the Navy VLF transmitter at NSS, Annapolis
MD. It was about 5 inches in diameter, was composed of perhaps 19 bundles
wound on a hemp core, each bundle with 200+ strands of #32 wire. The thing
carried 800 kilowatts of rf power at 17 kc. IF all fails for you, Fair Radio Sales has
replacement R-390A transformers for moderate prices.
Date: Wed, 31 May 2000 14:48:18 EDT
From: Bobdsmith@aol.com
Subject: Re: [R-390] Z201 problem

Barry, you didn't say how much wire is still sticking out of the coil but I think all
you may need is an asprin. No I am not kidding. Take an asprin tablet and place
it under the litz wire. Get a ball of solder on a hot soldering iron and use it to
press the litz wire into the asprin tablet. The wire will be stripped and tinned all
in one operation. Then you should be able to easily solder another wire to it. Do
this in a well ventelated area as the fumes are very unpleasent if they go up your
nose. --- Good Luck----
Date: Wed, 31 May 2000 20:02:25 -0400
From: "Tetrode" <tetrode@sprynet.com>
Subject: [R-390] non A Resistor R554 --- IF module schematic error?

Is there an error on the R390 schematic for resistor R554 in the IF module? It
shows it as a 2200 ohm (to Z503), but in the deck I'm working on and in another
I checked there is a 470 ohm 1 watt there. Didn't see anything mentioned in the
MOD table about it either.
IF deck tips                                      page 31

Date: Wed, 12 Jul 2000 19:52:49 -0400 (EDT)
From: Norman Ryan <nryan@duke.edu>
Subject: Re: [R-390] Panel Metering

You're getting warm, sorta. Front jack is the diode load. AGC line is what
you're interested in. Just to be sure it isn't a B+ blocking cap (C553) that's
studying eating up your filters, power down until you pull the rig and check it
out. Got your manual?
Date: Wed, 12 Jul 2000 20:01:57 -0400
From: "Ronald Reams" <wa4mjf@worldnet.att.net>
Subject: Re: [R-390] Panel Metering

Yep, there is a disk cap on FL502 that not on schematic. Also, that the markings
on FL-502 are really different than the other three. Is that something Rick adds. I
note he put a resistor in place of ballast.
Date: Wed, 12 Jul 2000 22:14:25 -0400 (EDT)
From: Norman Ryan <nryan@duke.edu>
Subject: Re: [R-390] Panel Metering

Is that disk cap inside the filter cover? That would be C512 on the schematic.
Could be FL502 is a replacement. It should have Collins part number something
like 522-9163-002. (Last digit sometimes varies.)
Date: Thu, 13 Jul 2000 02:56:36 -0400 (EDT)
From: Norman Ryan <nryan@duke.edu>
Subject: Re: [R-390] Got it out of console and cabinet

> 1 J512-6 to gnd infinity passed
> 2. I/O FL-502 short same-same FL-503 and FL-504 FL-505 65 ohms UH-OH
> 3. Terminals of FL-502 to gnd infinity passed

Did you make the tests while turning the BANDSWITCH knob (or shaft)? Step 1
resistance reading should be infinity at any position. Otherwise, one or another
filter may be shorting or resistive to ground. I THINK, but don't know for sure,
that step 2 should short unless BANDSWITCH is set at the filter under test.
Consider disconnecting one lead from each end of the 2 KC filter and measuring
resistance. It's most likely suspicious. You're getting closer... While the deck is
on the bench, this would be a good time to replace all paper caps outright and
any resistors over ten percent out of spec. The oil cap can usually is OK, but
check for excessive leakeage. (This is for the slow AGC setting and has no
bearing on the above problem.)
IF deck tips                                      page 32

Date: Thu, 13 Jul 2000 11:05:54 -0400
From: "Ronald Reams" <wa4mjf@worldnet.att.net>
Subject: [R-390] Moving Along

Found pin 2 of J512 pin 2 62 K instead of infinite. Looks as if Rick did not replace
C-553 gonna look in junk box for one now
Date: Thu, 13 Jul 2000 14:43:59 -0400 (EDT)
From: Norman Ryan <nryan@duke.edu>
Subject: Re: Fw: [R-390] C-553

J512-2 should read 50K to ground. 62K not serious problem-- could be one or
more out of spec resistors. Is 62K consistent at each setting of BANDSWITCH?
What shape are C510 and C513 in? (Silver micas across FL502 terminals.)
Trimmer caps OK? anything different about FL502? Does its part number

Here are the resistances for J512:

1. Inf       (not used)
2. 50K        Switched RF-IF B+ line
3. 54K        Limiter circuit7
4. 500K        AGC rectifier output
5. Inf       Diode load
6. Inf       AGC line
7. Inf       Audio output to AF deck
8. Inf       Ballast tube
9. Inf       Limiter circuit
10. 440K Limiter circuit
11. Inf       BFO B+
12. 27        Carrier meter -
13. Inf       AGC switch
14. 0 to 20 Carrier meter +
15. 132K AGC switch
16. 100K        Cathode bias line
17. 0        Chassis ground
18. 0          "     "
19. Inf       Ballast tube
20. .5       Filaments                                         Don't give up.
Date: Thu, 13 Jul 2000 18:08:51 -0400
From: "Ronald Reams" <wa4mjf@worldnet.att.net>
Subject: [R-390] Fuses blowing

Took out filaments of the 26Z5s, Replaced and with IF deck out of circuit all B+
normal and 150 VDC reg OK.
IF deck tips                                      page 33

Date: Thu, 13 Jul 2000 19:10:22 -0400
From: "Ronald Reams" <wa4mjf@worldnet.att.net>
Subject: Re: [R-390] Fuses blowing

Don't know, Joe. Everything was FB until I decided to work on the filter
problem. I have a 68 K gnd on pin 2 of IF deck. -35 sez should be infinite.
Norman sez 55k. Everything does OK with out IF deck so gonna be sure it OK,
even if it has to go to Chuck. 26Z5s getting harder to find than hen's teeth.
Date: Thu, 13 Jul 2000 21:08:57 -0400
From: twleiper@juno.com
Subject: Re: [R-390] Fuses blowing

> Don't know, Joe. Everything was FB until I decided to work on the filter

Watch your handling and retrace your steps. I took an IF deck out once to
replace C553, and after I put it back I had no AGC action. Took the jumper off
the back panel and saw that the the AGC line was showing short to ground
which opened the moment I unplugged the IF deck. Turned out I had pressed
the ground side lead of a disk cap against the AGC line at a solder post while
handling the deck... By the way, I think it is crazy to swap those filters too. If it
were me I think I would remove the filter and clip in a couple open ended test
leads, then twist them together as a gimmick capacitor, just to get some signal to
pass through (tighter twist, greater passband) and see if things behave logically
in the three narrow positions...what you need is more data, and, by now,
perhaps some rest.
Date: Fri, 14 Jul 2000 03:55:01 -0400 (EDT)
From: Norman Ryan <nryan@duke.edu>
Subject: Re: Fw: [R-390] C-553

First thought I had after reading your post was "Gak!! Not another brain fart!"
Have made mistakes before in earlier posts and have resolved to improve--
there's no going back to edit the r-390 archive, after all.

Hurried over to my TM 11-5820-358-35 which I keep in the climate controlled
bullet-proof glass cabinet along with the Gutenberg Bible and saw that lo, your
reference to para 41 is correct-- infinity on J512-2. Heck of it is I got my reference
from para 56c, page 98-- 50K on J512-2. So which is right? Checked my FB
newly restored IF deck and got 52.4K in all positions of the BANDWIDTH
switch. Wonder what sayeth the Y2K manual? Anyone caught that one?
IF deck tips                                      page 34

Date: Fri, 14 Jul 2000 19:13:41 -0400
From: Al Tirevold <tirevold@mindspring.com>
Subject: Re: Fw: [R-390] C-553

R390A-Y2k sayeth "50k" in Table 5-7, paragraph 5.5.7, Page5-34 of the 2000-May-
29 vintage......the 52.4k you found is close enough....
Date: Fri, 14 Jul 2000 19:34:34 -0400
From: "Ronald Reams" <wa4mjf@worldnet.att.net>
Subject: Re: Fw: [R-390] C-553

my -35 sez J512-2 Infinite.
Date: Sun, 20 Aug 2000 11:07:50 -0700 (PDT)
From: Tom Marcotte <courir26@yahoo.com>
Subject: [R-390] Z-503 Woes . . Repairs In Situ?

I've got a nice EAC on the bench that is very good shape, except that the pesky
Z-503 is open (of course, AGC does not work).

Now I'd rather take a bullet than replace this thing. Seems that nearly every
component in the IF deck is hung off of this thing. Has anyone ever removed
just the core, leaving the frame behind, and replaced the core of Z-503? Seems
like it is possible with copious amounts of epoxy. I've got a couple of spares, so I
could try it once or twice before making a doorstop of this IF deck. Comments
and counsel please!!!
Date: Sun, 20 Aug 2000 20:42:24 EDT
From: PABigelow@aol.com
Subject: Re: [R-390] Z-503 Woes . . Repairs In Situ?

Yes, repair of Z503 is possible. It is easy enough to remove the coil assembly
with the core. Removal of the outer core is possible by using a heat gun and
*carefully* sliding the outer core off the coil. The coil is would with litz wire in
three equal and equally spaced sections. Unwind the wire, fix the break, rewind
the coil (use a washer to keep proper spacing between the sectons).

Use the heat gun once again to aid in slipping the outer core back onto the coil
Replace the coil assembly as before. Make sure the replaced wires do not touch
the outer can.
Date: Sun, 20 Aug 2000 21:22:42 -0400 (EDT)
From: Norman Ryan <nryan@duke.edu>
Subject: [R-390] R-390A Z503 Repair (fwd)

I liked Paul Bigelow's earlier post about this problem and saved it. I may have
redacted it so as to conserve disk space and hope Paul doesn't mind.
IF deck tips                                      page 35

            - ---------- Forwarded message ----------
From: pbigelow@us.ibm.com

The Z503 (AGC tuned circuit) was open when I acquired my R-390a. With
assistance from a friend, our repair steps:

1) Remove Z503 coil assembly (just the winding assembly, not the WHOLE
 a) Remove cover.
 b) Unsolder connecting wires to coil form -- make note of wires.
 c) Unsolder wire posts that hold cover that hold coil form in place.
 d) Remove coil form.

2) Using a heat gun, soften the resin that holds the outer ferrite cup:
 a) Work cup off carefully while it is hot-- the resin hardens quickly.
 b) Three wound sections are present.

3) Locate break using a very fine point and DMM.

4) Unwind offending section:
 a) Make note of direction of unwind.

 NOTE: For me it was the middle section -- unbelieveably, there appeared to be
a little corrosion in the wire

5) Repair break.

6) Rewind section. To rewind middle section coil:
 a) Place circular spacers on both sides of "good" coil sections so that spacing and
form of rewind become close to the original-- use a rubber washer, for example.
 b) Rewind in proper direction.
 c) Remove spacers.

 NOTE: Not having a coil winding machine we could not match the winding
pattern of the the original coil. Nevertheless, it didn't look too bad.

7) Use heat gun to resoften resin in ferrite cup and slip it back over sections.

8) Glue form back into place.

9) Resolder coil wires back in place-- ref 1b.

10) Place coil form support back on top.

11) Solder wires back onto top support.

12) Replace cover.                                                     l Bigelow
IF deck tips                                      page 36

Date: Sun, 20 Aug 2000 22:15:14 EDT
From: PABigelow@aol.com
Subject: Re: [R-390] R-390A Z503 Repair (fwd)

Hey Norman, Thanks for saving that old post! Fixing that Z503 was bit of work.
What bothered me though was that the Litz wire had small bits of greenish areas
throughout its length as if the copper was corroding in a bunch of little places. I
would have thought that corrosion would be the LAST thing I would see -- with
all that epoxy.
Date: Wed, 23 Aug 2000 10:40:35 -0700 (PDT)
From: Tom Marcotte <courir26@yahoo.com>
Subject: [R-390] Z-503 Swapout
         I'd like to thank Chuck Rippel and all the other folks who replied to my Z-
503 question. In summary, it is possible to swap out just the "guts" of Z-503 and
not remove the whole assembly.To do this:

A) Remove the can       B) Remove the nuts under the can top; C) Unsolder the
long skinny stiff wires from the square top piece, also remove the coil
wires.4)remove the square top piece
D) wiggle and lift out the old assembly

When installing a new assembly, make sure to glue it in so that the possible
torque of the slug whilt being adjusted is resisted by something.
Date: Mon, 4 Sep 2000 16:15:50 -0500
From: "Scott, Barry (Clyde B)" <cbscott@ingr.com>
Subject: RE: [R-390] Several questions...

Oops. It's an R390A and those transformers should be T501, T502, and T503, not
T305, etc. Working from my memory is a very dangerous thing sometimes...
BTW, I looked at the schematic at lunch and that resistor replacement evidently
was part of a mod. I checked the resistance from cathode to cathode of V501 and
V502 and got about 660 ohms (there is a 100 ohm resistor (R513) in series with
V502's cathode so this measurement will give the total of R504, R513, and L501),
so I must have the mod already made in this IF deck.
Date: Sun, 10 Sep 2000 20:08:23 EDT
From: PABigelow@aol.com
Subject: [R-390] Y501 -- 455kc crystal

Not much is written about Y501 (455kc crystal) in the manual. Is its purpose to
act as low cost filter in front of the 1st IF amp? If so, could R-390a performance
be improved by replacing the crystal with a high quality ceramic or mechanical
filter (centered on 455kc) ?
IF deck tips                                      page 37

Date: Sun, 10 Sep 2000 18:33:45 -0500
From: "Dr. Gerald N. Johnson, electrical engineer" <geraldj@ames.net>
Subject: Re: [R-390] Y501 -- 455kc crystal

Paragraph 62, page 57, TM-11-856A covers the crystal filter fairly well Its only in
the circuit and provides the selectivity for the 0.1 and 1.0 kHz bandwidths. Then
page 60 shows that the 2 kHz mechanical filter is used with the crystal filter on
those two narrower bandwidths.
Date: Sun, 19 Nov 2000 12:24:01 -0600
From: "Bill Hawkins" <bill@iaxs.net>
Subject: RE: [R-390] C275 and more

> ... One might achieve a spot weld with a fairly simple holding jig to hold the
wire against its disk and then dissipate the stored energy in some 100 mfd
capacitor charged to 450 volts (+/- 300 volts depending on the required energy)
through that joint.

That "+/- 300 volts" is the tricky part.

I did some spot welding of fine wires back in the early 60's (blasting cap bridge
wires a few mils in diameter). When anything in the process changed, it was
necessary to run a series of trials to determine pull strength versus energy. A
different wire size could mean using a different capacitor to get the voltage
down. Variables in the trials included electrode size and pressure as well as

This is definitely not something to try on a valuable part on a one shot basis.
Sure, you could start low and work up, but each time you heat the joint you
change the surrounding metal structure.

Now, if there was someone out there who used to weld the wires to assemble
mechanical filters, we might not have to run a thousand trials to find the right
energy. Or if we had a thousand volunteers to zap their mechanical filters ...
Date: Fri, 01 Dec 2000 23:42:33 -0600
From: "Dr. Gerald N. Johnson, electrical engineer" <geraldj@ames.net>
Subject: Re: [R-390] R725/URR audio problems

Poor AGC comes from low AGC if gain or leaky AGC bypass capacitors
(including the large time constant capacitor). Have you replaced the paper
capacitors? Leaky paper capacitors will lead to many problems with marginal
IF deck tips                                      page 38

Date: Mon, 4 Dec 2000 13:59:33 -0500
From: brumac@juno.com
Subject: [R-390] I F Cap Identification Help Needed

This may sound a little childish, but I have a cap in the IF deck that I am having
trouble identifying. It is between C533 and C534, just behind the BFO bellows,
and it goes to pin 3 of V505 and ground. The chassis markers on the side don't
seem to be properly located and make ref to C538. The Y2K manual photo on
page 6-53 calls it C551, which is located elsewhere. The value is 0.1 mfd. FYI,
all the BB's were leaking and yes, ODs are going in
Date: Mon, 4 Dec 2000 14:19:00 -0600
From: "Scott, Barry (Clyde B)" <cbscott@ingr.com>
Subject: RE: [R-390] I F Cap Identification Help Needed

Not childish. Sounds like that's C538, a 0.1uF from the heater to ground. Look at
the heater area of the schematic for this cap. Lots of fun replacing these three
caps, especially with higher voltage ODs. I think mine are 600V. Pretty
cramped, but it can be done. Take care that you place it such that the bellows still
have room to move freely.
Date: Mon, 4 Dec 2000 15:19:27 -0500 (EST)
From: Norman Ryan <nryan@duke.edu>
Subject: Re: [R-390] I F Cap Identification Help Needed

On the schematic C538 (0.1 uf) is located in a small dotted line square near the
power supply diagram. Pin three of V505 is one leg of its heater filament.
Date: Mon, 1 Jan 2001 10:43:16 -0800 (PST)
From: "Tom M." <courir26@yahoo.com>
Subject: [R-390] 390 IF Deck in 390A

Walter, In answer to your questions, putting a 390 IF deck in the 390A is not too
tough to do. First, get a 390 IF deck. Then all you have to do is rewire the 25V
filaments for 6V filaments (except for the ballast/BFO/PTO string) and then
make a couple of MB->BNC adapter cables. You also need a dropping resistor
on the B+. The deck will drop right in (except the screws in the 390 deck are
larger than the holes in the 390A frame) I wrote up a complete procedure for
Electric Radio magazine on this. Contact Barry Wiseman at er@frontier.net for
the Dec 2000 issue.

Pros- excellent sound from your 390A, esp when using an outboard amp at the
diode load (this is why I did it) IMHO. Listening for hours does not wear one

Cons- finding a 390 IF deck, inferior shape factor for serious DX (drop in your
390A IF deck for that). There are no irreversible mods to the 390A, not the case
for the 390 IF deck.
IF deck tips                                      page 39

Date: Tue, 2 Jan 2001 06:32:48 -0500
From: "Walter Wilson" <wewilson@knology.net>
Subject: Re: [R-390] Cap. Leakage on AGC Line?

>Still chasing my low AGC and carrier meter problem here. With a huge 10
microvolt signal I >can't get more than about minus 4-5 volts of AGC and barely
3/4 scale carrier reading.

10 uV is not huge to me. 10 uV shows only about -2 volts on the AGC on my
chart. 10,000 uV or 10 mV should give you about -9 volts DC. Did you mean 10

> I did the resistance check outlined in the maint. manual, checking from each
>module connector to ground. In the RF Module, I found an apparent
>discrepancy. On pin E of J205, the manual says this should be infinity. This is
>the AGC line to the RF stages. Instead, I measure a constant 1.7 megohms
>(with the tubes pulled)! Could this be a leaky or shorted capacitor somewhere
>in the AGC in the RF Module? But before I embark on removing the RF
>module (ir looks horrendous), in case there's a typo in the book, would
>someone be so kind as to measure the same pin (on the RF module) to ground
>in their radio (390A) and tell me what they read? I used a high impedance
>DMM. If everybody comes back saying "infinity" then here we go with front
>panel and RF module -- help!

If you meant pin E of J208, the book is indeed wrong. This has been an error
from earlier manuals that propagated down the line. Even the AGC schematic
(which is not in the Y2K manual but exists in TM-11-856A, page 183, Figure 104)
has some incorrect values. This AGC schematic should show R201 as 270K
(instead of the 22K shown), and this schematic omits R234 which is 1.5 M and
parallels C226 to ground. These two will give you an impedance of 1.77 M to
ground. Your readings do not indicate any AGC problems in the RF deck based
on your resistance measurements. The troubleshooting tables are "usually"
pretty good, but when it doubt, trace the schematic and calculate it yourself. Are
there any problems with AGC voltage developed on the IF deck. Try removing
the AGC jumper on the back of the radio and measure AGC voltage on terminal
3. You will have taken the RF deck out of the picture. If the AGC voltage is still
low, you can isolate your troubleshooting to the IF deck.
Date: Tue, 02 Jan 2001 08:01:13 -0500
From: Jim Miller <jmille77@bellsouth.net>
Subject: Re: [R-390] Cap. Leakage on AGC Line?

In my depot maint. manual, under receiver overall gain test (section 42) it says
that if the AGC is -7 volts for an input signal of between 1 and 4 microvolts, the
gain is normal. I have been going by that as a reference. Is this another "typo" in
this manual (I have found a few).
IF deck tips                                      page 40

Date: Tue, 2 Jan 2001 08:15:51 -0500
From: "Walter Wilson" <wewilson@knology.net>
Subject: Re: [R-390] Cap. Leakage on AGC Line?

I was looking at a chart of AGC voltage versus signal input. It starts at about -2
volts for 10 uV and goes to -9 volts at 10,000 uV, drawing a straight line. On page
5-27 of the Y2K manual, step 19, it shows -4 VDC at the AGC terminal for 100 uV
of signal input. Translating that to carrier level indication, this would be about 60
dB on the meter (see step 17, same page).
Date: Wed, 3 Jan 2001 21:05:20 -0500
From: "Walter Wilson" <wewilson@knology.net>
Subject: Re: [R-390] Carrier Meter Adj Pot

I bought my last carrier adjust pot from Mouser for under $10. Spectrol
precision 10 turn pot with metal shaft, 100 ohms, Mouser part number 594-
Date: Mon, 08 Jan 2001 12:59:53 -0500
From: Jim Miller <jmille77@bellsouth.net>
Subject: [R-390] BFO Neutralization

When I switch the BFO on my 390A, the carrier level meter registers about one
to two units. When I switch it off it goes back to zero. I can dip this residual AGC
reading with the BFO Neutralization trimmer on the IF module but that's as low
as I can get it. Is this a normal thing? I just installed the SSB mod involving two
diodes (one across R547 and one across R546 to improve AGC attack), and a 47
pf capacitor in parallel with C535 (presumably to increase BFO injection). After
this mod, the carrier meter will rest at almost 3 markings on the scale, and the
neutralizing cap won't reduce it any more. Again, is this residual BFO signal
affecting the no-signal AGC level a normal thing?
Date: Mon, 8 Jan 2001 12:54:25 -0700
From: "Kurt" <radiouser@uswest.net>
Subject: Re: [R-390] BFO Neutralization

When I added a 47 pf cap across C 535 I experienced the same increase in the
minimum S meter reading. I have done this to two different radios and they
both behaved the same way. If others have had different results please speak up.
Date: Mon, 8 Jan 2001 18:47:59 -0500
From: "Walter Wilson" <wewilson@knology.net>
Subject: Re: [R-390] BFO Neutralization

I have the Lankford SSB mod installed, which added the 47 pF capacitor. I get
about 2 dB increase (2% of full scale) in carrier level with the BFO on with no
incoming signal (external antenna switch in another position). I can't detect any
change in the carrier meter level on strong AM signals when I turn the BFO on. I
IF deck tips                                      page 41

have not compared this to an unmodified IF deck, but 1 to 2 dB does not cause
me any grief.
Date: Mon, 08 Jan 2001 19:24:54 -0500
From: Jim Miller <jmille77@bellsouth.net>
Subject: Re: [R-390] BFO Neutralization

I was getting quite a carrier meter deflection with the 47 pf cap installed when
BFO was turned on, and it seemed to swamp weak signals, about 2-3 ticks on the
meter even after nulling with the neutralization trimmer. As an experiment, I
removed the 47 pf capacitor that was added with the SSB mod, and of course the
stray BFO signal dropped back to normal deflection. Additionally, the SSB audio
seemed just as intelligible without the cap (or the extra BFO injection), and
maybe a little more so. So I will run with only the partial SSB mod, that is the
diodes in the AGC to improve attack time. Must be something unique about this
SW IF module..
Date: Tue, 9 Jan 2001 06:05:45 EST
From: DCrespy@aol.com
Subject: Re: [R-390] BFO Neutralization

It is not normal. You were correct to dip the BFO nuetralizing cap. With the
AGC mod (I have done 3 radios with it), the S-meter zero should be the same
with or without the BFO. I have tried it both with and without the 47 pf cap and
find no big difference. A long shot, but maybe you should pull it and try again.
The other obvious question is about the polarity of the diodes. After that, I'd say
you are clearly getting some BFO leakage to the AGC amp/detector. The
neutralizing cap should dip in two places during a 360 degree rotation. If not,
something is wrong in that circuit. Otherwise, unfortunately, I don't know
where to suggest to start. Perhaps lead dress from the mod, or a bad final IF or
AGC amp tube (BFO getting through it)???

Let us know what you find.
Date: Wed, 10 Jan 2001 14:09:45 -0800 (PST)
From: Dick Davis <enigma_y_2000@yahoo.com>
Subject: [R-390] 390A IF Module Mod J. What is it?

I'm trying to find information on what the "Mod J" is for the R390A I.F. module.
The mod isn't listed in my T-11-856A and if it is on the Radio Era R390A archive
CD-ROM, I can't find it. Tracing the circuitry, I find some changes around the
Carrier Level Meter circuitry. Does anyone have information on this, or where I
can find information?
IF deck tips                                      page 42

Date: Wed, 10 Jan 2001 21:11:04 EST
From: DCrespy@aol.com
Subject: Re: [R-390] BFO Neutralization

I just thought I should reepond again, as in my first note I'd said that in my three
radios I had no meter movement when the BFO was turned on. I'd never
noticed until the posts from some of the other guys here, but my carrier meter
DOES move upward slightly when the BFO is turned on (after the mod). I still
stand by my observation that 3 divisions movement on the meter scale is way
too much, and is not normal. My meter just wiggles (less than a needle width
upward). I would still try the items I'd suggested. You are getting a LOT MORE
than normal BFO leakage to the AGC detector. I hope you have had some luck
figuring this one out! Let us know what you find. 73, Harry KG5LO
Date: Wed, 10 Jan 2001 22:29:13 -0500
From: "Jim Miller" <jmille77@bellsouth.net>
Subject: Re: [R-390] BFO Neutralization

Thanks to all who responded to me "the newbie" on this. To review, my
problem is that my carrier level meter jumps about one unit when I switch the
BFO on, due to BFO leakage into the final stages of the IF. Neither the RF gain
nor the IF gain pots have any affect on this. When I added the simple SSB mod
(2 diodes and 47 pf cap), the "no signal" carrier meter reading went up to 2-3
meter units when the BFO was on. I've looked some more into this but have no
real resolution yet. I received one reply that said this upward meter movement
with BFO is normal...his moved upward also when he turned his BFO on. Then
another who said it was not normal...and then another saying his showed maybe
just a meter width movement. I've since replaced my meter pot and the meter is
behaving a little better, but it still moves about one meter unit when I turn the
BFO on (that's without the SSB mod ). With the SSB mod (that adds a 47 pf cap in
parallel with the BFO injection cap.) I get what looks like 2-3 unit jump of BFO
residual carrier on the meter. I checked R522 inside T503 (as was suggested by
Walter Wilson I htink, and it's still there, hasn't been clipped out. All the IF cans
seem to peak up OK during alignment. The BFO neutralizing cap does appear to
produce a null in this residual BFO bleed thru but not all the way to zero, and I
do appear to get 2 peaks (or dips). So I am running the SSB mod with just the
AGC diodes and not the 47 pf cap. Signals sound OK but maybe a little distorted
due to the lower BFO injection. I am still at a loss as to the cause...maybe some
manufacturing differences in the various IF modules out there. Or do you
suppose I could have misaligned the IF stages causing the neutralizing cap to
have reduced effect?

I'll probably just live with it for now and go back to it later. I replaced the carrier
meter today and the carrier pot and now the meter seems to respond in a much
more healthy manner. This is an incredibly hot and impressive receiver, well
designed with plenty of gain. And not as difficult to maintain as it first appeared
to me. Front panel has been removed with no problem. I've had the crystal
oscillator module out and cleaned it, done maintenance (cap replacement etc) on
IF deck tips                                      page 43

the AF module, ...almost completely recapped the IF module,...next comes
removal and a general inspection and cleaning of the RF module, then PTO end
point and linearity adjust when I get the courage up.
Date: Thu, 11 Jan 2001 09:31:58 -0600
From: Roy Morgan <roy.morgan@nist.gov>
Subject: Re: [R-390] BFO Neutralization

... This is an incredibly hot and impressive receiver, well designed with plenty of

THAT may be your clue. Have you done an IF gain setting procedure as
described on Chuck Rippel's web page? It could be that the "gain distribution"
in your radio is out of whack. Gain distribution, means the relative gain in the
various stages. If the IF section has too much gain (VERY easy to have) then
some stages will be operating at too low a gain. This idea may not be well
founded, since the BFO is injected after the stages of the IF that have gain.. I do
not have schematics and such here to reason out the situation. BUT, I suggest
you do that procedure - it is quite easy - and then see what you get.
Date: Fri, 12 Jan 2001 05:05:46 -0500
From: "Jim Miller" <jmille77@bellsouth.net>
Subject: Re: [R-390] BFO Neutralization

Thats what I'm starting to think...However, I still get the meter deflection with
BFO on even when the IF gain pot is all the way down. It's bleeding into the
very last stages, maybe the AGC amplifier. One thing comes to mind... is
everybody's carrier meter the same sensitivity? When I got my 390A the carrier
meter was a dog, the calibrator registered only about 3 units. After a new meter
(actually a NOS glow in the dark original), some serious recapping of the IF, bug
fixes and alignment, i now get mid scale to slightly over on the 100 khz calibrator
signal. So if my meter, being original now, is hotter than others who have
commented on this BFO leakage, that could explain why others don't see as
much deflection when the BFO is turned on. Also, I am careful to zero the meter
with the BFO turned OFF and the RF gain on the front panel all the way off, and
no antenna. Then if I turn the BFO on, I see the deflection about 1 meter unit,
maybe slightly more. If you zero your meter with the BFO on or RF gain up, I
think you may get a false zero, so turning the BFO on and off won't be as
noticable on the meter.
Not gonna worry about it anymore for now...now have bigger problems..went
into the RF deck and cleaned it, replaced C275 with an orange drop (it was a .033
black beauty..yes it really was .033 and not .0033!), a bad resistor, etc, cleaned it
and replaced it and worked great...until I started lubing the gears and slides and
then she quit...the 1st oscillator stopped. I suspect I got some oil somewhere it
shouldn't be...Any ideas? Wish me luck\73 Jim N4BE
IF deck tips                                      page 44

Date: Fri, 12 Jan 2001 06:36:43 -0500
From: "Barry Hauser" <barry@hausernet.com>
Subject: Re: [R-390] BFO Neutralization

Here are some thoughts, barely 2 cents worth:

1. The meters vary. The NOS one you got might not be exactly original spec.
Remember, the originals have a DC resistance of only 17 ohms -- very rare.
There are a lot of original looking subs that have higher resistance. Don't take an
ohmmeter to it yet -- check Dr. J's post about how to check the DC resistance. If
it is original/on spec, then you might want to check the resistors in the bridge
circuit for the meter to see if they were either subbed out or drifted. If the meter
is not a 17 ohm job, then you have to change the bridge resistors to get the right

2. Before you start looking for esoteric problems due to oil in the wrong place,
check tubes. Also check if you didn't completely tighten a connection here or
there. (or if something snapped inside a plug shell). Then you might just check
the cap you just put in although that's unlikely. One of two or three variants of
Murphy's Law may be operative -- (a) while you're fixin' one thing, 'nother will
break, and or (b) high failure 50 year old part with 25 years to go replaced by
bright shiny new part, one out of 10,000 that will fail after 2 hrs. or just after you
screw everything back together. For example, you've been moving things
around a bit, and sometimes a borderline tube will fail after being jounced, so it's
a coincidence but not exactly -- what the medical profession calls "complications".
How much oil did you pour in there? The ratio is one quart to a couple
thousand radios, not the other way .. nevermind. Seriously though, you'd really
have to overdo it quite a bit for that to be the cause. Of course, if you spot an oil
slick under the radio that runs down the bench onto the floor, then maybe...

Could also be you're fussing about with that R-390A way too much. Some are
verrrry sensitive, pick up on those cues -- nervous sweat, shaky hands, facial
expressions, body language, cussing, groaning -- and get upset. Ever wonder
why there's such a big divide in experience with these things? Some don't fix it
til it breaks guys blissfully run with original caps, no variac or bucking
transformer for 30 years with no problem and have the original ballast tube.
Other guys replace every cap and questionable resistor -- confirming they're all
bad -- and still have more to do. Could be attitude or maybe even mojo or
something. Did ya' know if you look too hard at those BBOD's they'll split? It's
a little known, but proven, self-fulfilling prophecy. Those who take a real hard
close look at 'em invariably find split ones, whereas the nonchalant types don't.
IF deck tips                                      page 45

Date: Fri, 12 Jan 2001 06:43:00 EST
From: DCrespy@aol.com
Subject: Re: [R-390] BFO Neutralization

One quick thought.. are you sure that you have a 6AK6 and not a 6BA6/5749 in
at V504? This could account for back leakage of the BFO signal. Since the
pinouts of the tubes are the same, the substitution would appear to work.. but....
Date: Fri, 12 Jan 2001 17:39:29 -0500
From: "Jim Miller" <jmille77@bellsouth.net>
Subject: Re: [R-390] BFO Neutralization

I checked...it' is a 6AK6. Thanks for the idea though. Right now the BFO thing
has been hugely overshadowed by something I broke in the RF deck and can't
find yet.
Date: Sat, 24 Oct 1998 11:54:18 -0500 (CDT)
From: Bill Hawkins <bill@iaxs.net>
Subject: Re: [R-390] Caps and the VTVM.

DMM's have pretty high impedance. The key would be whether or not the
sound from the radio changes when the DMM lead is applied to the AGC. Since
AGC voltage is within a feedback loop, you also need to know precisely how
much signal you are injecting. The error at the signal generator could be much
larger than the error from the DMM. But, the most common cause of low AGC
voltage is leaking caps - *if* the other things that affect gain are OK, such as
tubes and alignment.
Date: Sat, 24 Oct 1998 12:35:45 -0500
From: "Dr. Gerald N. Johnson, P.E." <geraldj@ames.net>
Subject: Re: [R-390] Caps and the VTVM.

DMM SHOULD be high impedance but that's not guaranteed. With
contemporary solid state circuits tending to be much lower impedance than
ordinary vacuum tube circuits, some makers and vendors of DMM take short
cuts in input impedance because it eases their design and production tasks and
doesn't mess up readings in many circuits. That being said, its important for
trouble shooting to always KNOW the test meter impedance AND the meter
impedance used to make the normal voltages chart in the shop manual.
Otherwise you WILL be confused by some voltages showing different values
(higher or lower according to the meter impedance) than the table. Some
voltages will read right, some will be different.
IF deck tips                                      page 46

Date: Sat, 24 Oct 1998 12:27:44 -0700
From: Philip Atchley <ko6bb@elite.net>
Subject: Re: [R-390] Caps and the VTVM.

That test point E402 is for the grid voltage on the Xtal Osc, you peak it when
tuning the trimmers. I found (at least on mine) it is very sensitive to loading,
either capacitive or resistive. I used a Heath VTVM which has a 1MOhm
isolation resistor in the probe, still loaded it some. So I put a 1 Meg resistor (very
short lead one E402 end) into the test jack then used my probe on that. Was able
to tune easier with less loading effect. (true 1 meg will change meter reading but
this is a "peak" adjustment anyway)
Date: Tue, 16 Jan 2001 20:12:42 EST
From: DJED1@aol.com
Subject: Re: [R-390] B+ Dropping Resistor, Paint, Etc.

It's possible that you can't cancel the BFO leakage after increasing the BFO
coupling cap because the neutralizing cap is not large enough. You could
probably check this theory if you can tell whether the lowest meter reading is
when the neutralizing cap is at full capacity. You could try shunting a similar cap
across the neutralizing cap. Just a theory, I haven't tried the Lankford
Date: Tue, 16 Jan 2001 23:00:32 -0500
From: "Jim Miller" <jmille77@bellsouth.net>
Subject: Re: [R-390] B+ Dropping Resistor, Paint, Etc.

Thanks for the idea...but when I look at the position of the rotary part of the
trimmer it appears to not be at its limit and I get two dips close to each other. So
it doesn't appear to be maxed out. It's not a bad thing but it just doesnt seem to
be nulling as far as it could. Copying of signals is fine. I have done half of the
Lankford mod, but did not add the 47 pf parallel cap yet, because of the BFO
bleed thru. I will eventually find it.
Date: Wed, 17 Jan 2001 21:42:35 EST
From: DCrespy@aol.com
Subject: Re: [R-390] B+ Dropping Resistor, Paint, Etc.

> It's possible that you can't cancel the BFO leakage after increasing the
BFO coupling cap because the neutralizing cap is not large enough. ...........

Interesting idea.

If you get two dips or nulls in less than 180 degrees of trimmer rotation, that is
not the problem (ie. there is a SPECIFIC value, not just the extremes, that
achieves minimum). Also, the trimmer balances the input and output of the 4th
IF. I believe it is designed to offset the capacitive coupling in the final IF tube that
could lead to leakage back to the AGC amp. It is well isolated by the final IF
IF deck tips                                     page 47

transformer from the BFO injection cap. In any case it should have little effect.
In my radios it has not been an issue.
Date: Wed, 17 Jan 2001 23:01:02 -0500
From: "Jim Miller" <jmille77@bellsouth.net>
Subject: [R-390] Re: BFO Neut. Etc.

I haven't tried just replacing some IF tubes. They check good on the tester but as
you suggest there may be too much interelectrode capacitance in one or more of
the final IF tubes. Will try that. It's more of a curiosity than a real hinderance to
receiving...the radio receives beautifully. Now, Stand by guys, I'm about to start
adjusting end spread and linearity on this Cosmos PTO next.
Date: Fri, 19 Jan 2001 14:46:05 -0800
From: "Roger L Ruszkowski" <rlruszkowski@west.raytheon.com>
Subject: Re: [R-390] quest on modifications

- - what is the sense of stagger tuned 455kc if filters (453-455-457kc)
- - are there experiences in cutting out the 455kc filter resistors in T501toT503?

Do not cut the resistors out of the R390 IF deck. It gets down to 2KC in the
2KHZ switch setting and 100 Hertz in the .1KHZ setting. Chopping the resistors
out just screws up the impedence match between the tube stages and you get
more loss from that than the change in band width that come from messing with
the resistors. Been there done that as school house bugs for the new students to
trouble shoot as part of their class room training in the early 60's before the
R390/A went into the class rooms for training.

The stages are stagger tuned to get the right coupling between the primary and
secondary stages of each IF can. You can get a hell of a lot more out of the IF
deck R390 or R390/A by aligning them to the manual and then swapping tubes.
The noise level and gain in the tubes is much greater than the changes in the
transformers. Good mil tubes can be much better than other cheap tubes. Tubes
with hours on them can be less noisy than new tubes. A zippo applied to a tube
can do a lot for its noise. Heating the filaments on the tube tester do not work
the same as a zippo applied to a tube. go figure. With 455KHZ at 150 UV in you
better be getting 1/2 to 7/8 watts out and 30db signal plus noise to noise out of
the IF deck and audio deck with -7 volts on the diode load. Roger KC6TRU
IF deck tips                                      page 48

Date: Sun, 21 Jan 2001 19:13:08 -0500
From: Al Solway <beral@videotron.ca>
Subject: [R-390] IF Gain Adj. Pot R519

My recently restored R-390A has satisfactory sensitivity of less than 0.2uV on all
bands except band 3 and below where it is less than 0.3uV. Band 7 is 0.35uV. My
question concerns IF Gain Adj R519. After alignment and tubes changes that
improved performance the final position of R519 is at about 80% of max. I used
the procedure that is on Chuck Rippel's site to set R519. It is at this position that
get the best sensitivity using Chuck's procedure for measuring sensitivity. Is this
a normal position for R519 at 80% of max.
Date: Sun, 21 Jan 2001 19:00:19 -0700
From: "Kurt" <radiouser@uswest.net>
Subject: Re: [R-390] IF Gain Adj. Pot R519

I wouldn't worry about the position of the gain pot. The sensitivity you are
measuring is pushing the limit of the receiver and Chuck's method is designed as
to use the minimum amount of gain to get the best useable sensitivity.
Date: Sun, 21 Jan 2001 20:36:22 EST
From: Llgpt@aol.com
Subject: Re: [R-390] IF Gain Adj. Pot R519

Exactly Kurt, although most are set somewhere between 75 - 80 % YMMV
depending on the particular receiver condition of tubes etc.
Date: Tue, 23 Jan 2001 09:03:41 -0800 (PST)
From: "Tom M." <courir26@yahoo.com>
Subject: [R-390] Zero Beat, How To

The question came up today as to how one might set the BFO for use as a zero
beat. Here is what I do after a long warmup:

1) tune to a local broadcast station.

b) set selectivity to 2 (or lower, your choice).

iii) measure your diode load voltage and tune for max (this puts your IF at the
center of the filter, supposed to be 455 kcs).

d) zero beat the bfo, and reset its knob to zero.

If the station is on an even hundred, then you can flip on the calibrator and
calibrate it. No need to use WWV (sorry Roy Morgan) as broadcast stations are
well controlled in frequency. The WWV signal is subject to fading whilst the
locals are not. This procedure is close enough for BA work. No Cesium atoms
IF deck tips                                      page 49

Date: Tue, 23 Jan 2001 17:17:32 -0500
From: "Barry L. Ornitz" <ornitz@tricon.net>
Subject: [R-390] BFO Zeroing

Rather than worry about using a counter or other test equipment to set the BFO
knob at the correct point, there is a much easier and more accurate method to
center the BFO within the receiver's passband.

Step 1: Pick which filter you desire the BFO to be centered in its passband. If you
are a CW operator, you will probably choose the 1 Khz bandwidth position. For
SSB reception, use the 2 kHz bandwidth filter.

Step 2: Tune the receiver to a point where there is no signal, just noise, with the
BFO off.

Step 3: Turn on the BFO and adjust it to the point where the noise sounds the
lowest pitched.

Step 4: Loosen the BFO knob, and turn it so the knob pointer is at the 12 o'clock
position. Loosening the knob usually moves it so turn the shaft to check that
you really have hit the lowest pitch position.

This method works because of the fact that white noise has a uniform frequency
spectrum. When you turn the BFO on frequencies on both sides of the BFO are
heterodyned down to audio. The highest frequency noise you hear will be
limited by the filter bandwidth. If the BFO frequency is off to one side of center,
you will have a wider bandwidth of noise. At the point where the noise has the
lowest sounding pitch, you have exactly centered the BFO in the receiver's
Date: Tue, 23 Jan 2001 20:47:21 -0500
From: "Tetrode" <tetrode@sprynet.com>
Subject: [R-390] Ultimate BFO Zero Beat

Can't resist.......here's what I do when a radio is on the bench......... First, I connect
my frequency counter to the IF OUTput BNC on the back of 390x. Then, I tune in
any strong unmodulated carrier, usually it's a 100 KC calibrator signal. (If there's
not enough IF level to drive the counter, then I switch the AGC mode to Manual
and purposely overdrive the IF a bit for some more output.) Adjust the KC main
tuning until the counter reads 455.000....... Turn on BFO, zero beat it to the test
carrier, and set the adjustment. I guess I like to do it this way because I know I'm
setting the BFO to a measured reference frequency instead of the center
frequency of the crystal filter. Yeah I know the crystal frequency will be close
but this is my particular flavor of flyspecks.
IF deck tips                                      page 50

Date: Wed, 24 Jan 2001 13:52:08 -0500
From: swlchris@juno.com
Subject: Re: [R-390] Ultimate BFO Zero Beat

I forgot to give an example of what is going on here. I'm sorry , that would be
causing some confusion if you all didn't know what was going on here I would
think. Ok.... The R390 is on and tuned to 9870. AM mode now ,no BFO on, it is
coming in about 20 or so on carrier meter on a transmission. Go to switch BFO
on and in the zero postion it is coming clear no warble or anything. If I tune
down 2 khz to 9868 I can't tune it in at all in SSB with the BFO. If I tune up to
9872 then if I tune the BFO to almost the -2 postion I can tune it in. So does this
mean that the BFO is off by a couple of khz from the 455 khz if? If so then I need
to return the BFO knob to get the 9868 to work on the - - side of BFO and 9872
to work on+ side of BFO? Or is this a nonseperable BFO as in like a Sangean
803A where the BFO is just centered on the frequency and tuning off doesn't
really give USB\LSB?
Date: Sat, 27 Jan 2001 20:29:10 -0500
From: Thomas W Leiper <twleiper@juno.com>
Subject: Re: [R-390] Ultimate BFO Zero Beat

Tuning Hints 101

With it centered (theoretically) you will here both sidebands equally, such as if
you zero beat on an AM signal. At that same setting you would hear only one
sideband perfectly well if only one were present AND your selectivity was not
too tight. If you are listening in the "8kc" position and you are tuned to the
"carrier" or fundamental frequency of the upper or lower sideband signal, the
four kc bandwidth above and below the center frequency is enough to receive
either sideband without retuning and with sufficient fidelity.

The reason you would adjust your BFO up or down would be to offset a similar
adjustment you might make on your main tuning control to maximize the LSB
or USB signal by "centering" the tuned passband onto either sideband to improve
reception of that sideband while simultaneously reducing interference which
may be caused by signals on the opposite sideband or close to the frequency

In other words, start by cutting your passband down to two or one kc and tune
(with the BFO "off") onto the sideband signal until you get the maximum carrier
meter deflection regardless the intelli(garbled)ility, and then reduce the RF gain
until the meter deflections are minimal but present. Then you turn on your BFO
and adjust plus or minus until the signal is clarified. Finally, crank the RF gain up
to the highest level that leaves the most powerful signal undistorted.

When you are finished, you will see that you have, in fact, adjusted the BFO very
close to the same amount as the "offset" you tuned in the main tuning to
IF deck tips                                      page 51

maximize the sideband in the first step, usually about 750hz for voice
communication signals and 1 to 1.2K for higher fidelity broadcast SSB signals.

The actual amount you offset the BFO will be slightly affected by your filters and
crystal mixer frequencies, but the effect is minimal, and you will find that it really
has to do with the nature of the signal. In the case of your Non-A, the shape of
the passband does not have the sharp "skirt" of the cheap mechanical filter jobs
("A"'s) and you will find that you can adjust for "voice" verses "music" to a finer
degree without running into distortion caused by the skirt and ripples across the
passband inherent in the "cheap, reduced cost mechanical filter equipped R-390A
illegitimate step-children of the R-390" that infect the racks of so many
unfortunate subscribers to this reflector...but I digress.

For instance, a good exercise would be to tune to the USB signal of the Armed
Forces radio (around 6460 ?? I think) which has a USB voice channel and FSK or
RTTY on the lower sideband, as well as several other close and interfering utility
sigals. You will have to set your selectivity to 2Kc or less and offset tune to get
the voice signal out clearly. Set the selectivity to 1/10 Kc and "center" tuning on
the sideband before opening up to 1 or 2 kc for fidelity.

After some experience you will know where to set the BFO and bandwidth for
different types of signals, and you will simply tune the main tuning for clarity.
But it is important to learn how to do it the other way around so you can learn
the characteristics of your radio. However with tough signals, I will always find
myself adjusting tuning and bandwidth for maximum smoke before turning on
the BFO.
Date: Mon, 29 Jan 2001 10:40:25 -0600
From: "Scott, Barry (Clyde B)" <cbscott@ingr.com>
Subject: [R-390] Static problem

Someone's frying bacon in my radio. When I first turn it on, I get periods of
static that last for several seconds each. After a good warmup (30 min. or so),
this seems to subside completely. I also notice that if I flip the mode switch from
Stdby to AGC or from AGC to MGC, I get a buzzy, raspy, poping noise that lasts
for maybe 1/2 second. The noise is accompianed by a brief dimming of the panel
lamps. The If I slowly rotate the switch between these modes, I don't get this

Does it sound like the two problems I'm having are related? Is it possible dirty
contacts on the mode switch are causing the bacon frying noise? Does a gassy
tube sound this way? Is it indicative of another component going bad?

I've fed the IF to my TS440S tuned to 455kc and I hear the bacon-frying there.
Unless the noise is coming up from the mode switch, I suppose this might
indicate it's somewhere in the RF or IF modules. Does the bacon-frying noise I'm
hearing indicate anything common (other than breakfast may be cooking)?
IF deck tips                                      page 52

Date: Mon, 29 Jan 2001 11:56:12 -0600
From: "Dr. Gerald N. Johnson, electrical engineer" <geraldj@ames.net>
Subject: Re: [R-390] Static problem

Failing capacitors make those sounds. Failing potentiometers sometimes make
those sounds. Failing resistors can make those sounds. Unless the paper
capacitors have been replaced, I bet on them as the problem. Mica capacitors can
make those sounds, but its less common, ditto disk ceramics.
Date: Mon, 29 Jan 2001 12:02:32 -0600
From: "Scott, Barry (Clyde B)" <cbscott@ingr.com>
Subject: RE: [R-390] Static problem

All brown beauties have been replaced. It does, indeed, sound like a scratchy
variable resistor, but turning all the ones on the front panel don't affect it. I'm
hoping I'm not going to have to isolate a failing component in RF deck. That
thing is almost impossible to operate outside the box. :(
Date: Mon, 29 Jan 2001 13:09:46 -0500
From: jmille77@bellsouth.net
Subject: Re: [R-390] Static problem

I recently had an arc-over occur in the function switch (the switch that changes
from standby to agc to mgc etc., the one you note in your email I think) Several
of its contacts are used to switch B+ to different stages. It turns out that one of
these pins (I forget which one and don't have my manuals here) is very close in
proximity to the pin that connects to the break in relay. A carbon path had
formed over the years and was leaking. My receiver started popping last week
also. I suspect that in spite of good intentions that my use of cleaning spray may
have accelerated the breakdown. Eventually, it gave in completely (last week to
be specific) and nothing worked right, although the B+ fuse didn't blow. I had to
remove the switch from the panel (not necessary to unsolder the leads) and
inspect it carefully with a magnifying glass. There between two pins on the rear
of the switch was a nicely formed hole filled with black carbon that had formed
over the ages. I cleaned the little hole out as well as I could with a dental pick,
getting as much of the carbon out as possible, clean down to the virgin wafer
material, and filled it with a tiny dab of epoxy cement. Works good as new now.
Date: Mon, 29 Jan 2001 19:55:38 -0500
From: "Jim Miller" <jmille77@bellsouth.net>
Subject: Re: [R-390] Static problem

The thing that gave it away was the thin trail of smoke eminating from the
switch wafer!
IF deck tips                                      page 53

Date: Tue, 30 Jan 2001 10:29:03 -0600
From: "Dr. Gerald N. Johnson, electrical engineer" <geraldj@ames.net>
Subject: Re: [R-390] Caps,

<snip> A resistance check on an IF transformer would detect open coils, but not
open tuning capacitors. To detect open tuning capacitors, I'd check the
distributed capacitance with a Q-meter which will allow me to compute the value
of the tuning capacitor which is most often 100 pf. Open connections to mica
capacitors molded in the base is a common failure mode of IF transformers.
Windings can go open, most commonly from marginal stripping and soldering
of the wires at terminals inside. IF transformer with wire leads tended to be color
coded. Red for B+, green for grid... As I recall some Hammarlunds are prone to
loose the 1500 KHz IF transformer which hasn't been made for decades.
Date: Tue, 06 Feb 2001 11:36:32 -0600
From: "Dr. Gerald N. Johnson, electrical engineer" <geraldj@ames.net>
Subject: Re: [R-390] R-725 on eBay

The 390 type IFs were to have IMPROVED linear phase response, not the other
way around... It's the mechanical filters that have nonlinear phase response that
causes trouble in DF applications.
Date: Tue, 6 Feb 2001 10:48:22 -0800 (PST)
From: "Tom M." <courir26@yahoo.com>
Subject: [R-390] R-725 Extra Transformer/390 IF Conversion

I may have written that the extra transformer in the 725 was for the 500 series IF
filaments. In fact, the filaments in the 500 series IF are wired for 6V (except for
the PTO/BFO/ballast which are 25V). I recently converted a R-390 deck for use
in the 390A, and no extra transformer is required (by the way, it sounds great!). I
believe the extra transformer in the 725 is set up for hum-bucking at the PTO.
Wally, K5OP is the expert on this trick. Sorry for any confusion.
Date: Mon, 12 Feb 2001 07:58:45 -0800
From: "Roger L Ruszkowski" <rlruszkowski@west.raytheon.com>
Subject: Re: [R-390] Bandwidth Problem?

If it is a rock, the DC resistance should be very high.
Three ways to check a crystal.
One is to insert it into a test osc and see if it works.

Two is to feed it with a signal gen and look at it with a scope. When the gen is
tuned through its resonant frequency the scope output will increase.

Three set the generator up with modulation and tune the receiver to the
generator. Hang a meter on the diode load or audio out and watch it. Tune the
receiver up and down around the signal. The signal should peak across a small
dial range.
IF deck tips                                      page 54

As you go from 16Khz, 8Khz, 4Khz, 2Khz, 1Khz, .1Khz on the band width
switch then the receiver tuning range of the generator signal should get

Sort of like you are doing. You find that the 1Khz and .1Khz are just no more
narrow than the 2Khz switch setting. Which is you current problem.

If things are leaking around the 1KC and 0.1KC filters you maybe should be
looking for stuff soaked into the wafer sections of the can forms or wafer

Back when I use to dunk the whole deck into the degreaser machine. Little did I
understand the problems this was going to cause in these receiver 25 years later.
I was expecting them to all go to the scrap year and get replaced with better solid
state receivers.

Would some of you other Owner Operators like to offer some specific help for
Keith on this.
Date: Mon, 12 Feb 2001 16:02:45 -0500
From: "AI2Q Alex" <ai2q@adelphia.net>
Subject: [R-390] Bandwidth and "DX troubleshooting"

Let me offer a bit of "DX troubleshooting:"

The single 455 kHz quartz crystal used in the 0.1 and 1 kc. filter positions in your
R-390As is used in BOTH positions of the switch---so if the filter works in the 0.1
kHz position and not in the 1 kHz position, the problem isn't the crystal.

Keep in mind that the circuit is arranged to de-Q the xtal to change BW by means
of the rotary switch S501 and caps C501 and C503 in conjunction with R502 and
R503. Check the schematic diagram for this very simple series-parallel switching
configuration. It's shown in Fig. 3-4 on page 3-13 and is explained in paragraph of the 21st Century docs, and is also shown and explained in the TM.

The resistors are hand-selected during manufacture, so it's most likely that the
crystal and/or resistors have aged, causing the shift in circuit performance. If the
filter didn't work in either position, I'd buy the argument that it could be the
rock, but if it works in the 0.1 position, it's more likely the resistors or the switch

Check those components with your ohmmeter and you'll likely find the source
of this seemingly elusive bandwidth selection problem.
IF deck tips                                      page 55

Date: Wed, 14 Feb 2001 13:31:04 +0100
From: CLEMENS@ps.au.dk
Subject: [R-390] Filter choice affects S-meter reading

Perhaps a dumb question to the assembled wisdom of the group: Why would
the carrier-level meter reading on one R-390A invariably drop about 20-25 db
when I switch from the 8kc to the16kc filter? Not that I often do that, but still.
And this is no matter how spot-on the frequency I am. Is there something I can
adjust, or do I have to live with it? This is a Motorola from mid-1956.
Date: Wed, 14 Feb 2001 09:44:35 -0500
From: "AI2Q Alex" <ai2q@adelphia.net>
Subject: RE: [R-390] Filter choice affects S-meter reading

My guess, again using the fallible "DX troubleshooting" technique, is that

(a) you have a defective filter
(b) the contacts on BANDWIDTH selector switch S502/S503 are dirty/broken
(c) capacitor C507 or C516 are defective
(d) variable caps used in modified filter assys. C564 or C561 are defective.
(e) variable caps used in modified filter assys. C564 or C561 are mis-adjusted

Take a look at your filter assembly and try tweaking C564 and/or C561 using an
insulated alignment tool to see if that makes a difference. If it does, you can
realign those caps if you have a signal generator.
Date: Wed, 14 Feb 2001 14:14:24 -0600
From: Roy Morgan <roy.morgan@nist.gov>
Subject: Re: [R-390] Filter choice affects S-meter reading

>Why would the carrier-level meter reading on one R-390A invariably drop
about 20-25 db >when I switch from the 8kc to the16kc filter?

Your 16 KC filter is tired, worn out, had a failure, or is just plain busted. Get
another one.
Date: Wed, 14 Feb 2001 15:57:50 -0800 (PST)
From: Joe Foley <redmenaced@yahoo.com>
Subject: Re: [R-390] Filter choice affects S-meter reading

Yes, there is something to adjust, the trimmer cap on the filter. Also, check the
center contact underneath the trimmer, one of mine was shorting to ground and
making just the problem you found.
IF deck tips                                      page 56

Date: Sat, 24 Feb 2001 12:54:49 -0800
From: "khgrant@ix.netcom.com" <khgrant@ix.netcom.com>
Subject: [R-390] IF Module questions

Has anybody removed the BFO oscillator assembly? What is the procedure? It is
not listed in the Y2K manual. I need to replace R530 (22k) that is buried
underneath the BFO coupler. I need to get the coupler out of the way so's I can
replace said resistor (it measures 30k instead of 22k). If someone could explain
the procedure, I would appreciate it (and maybe add it to the Y2k manual).

I'm chasing a couple of problems:

1. The BFO seems to instantly shift in frequency a bit every once in a while. I'll
tune in a signal on a sideband and after a while the beat frequency jumps a bit,
requiring an adjustment to the BFO knob. Sounds like a bad cap or resistor to
me; thus my search. I'm not sure if R530 could cause a shift, but it needs

2. As I've reported several times, I'm having trouble with my filters. In
particular, 0.1 and 1 kHz bw positions dont seem to differ. In the 8 and
particularly the 16 kHz positions, I get a high-pitched audio oscillation
that's hard to describe. Sort of a 'zing' type effect to the audio signal. I hope I
don't have to replace my filters. Any ideas? It sounds to me like something is just
at the edge of oscillation, but I don't yet have a clue as to what.

3. Overall the audio in my rig is pretty crappy. Very 'muddy', indistinct. I've tried
some tube swaps so far, but havn't found the problem. I'll keep plugging away
at this thing. Any suggestions or words of encourgement greatly appreciated.
Date: Sat, 17 Mar 2001 16:12:00 -0800
From: "khgrant@ix.netcom.com" <khgrant@ix.netcom.com>
Subject: [R-390] Re: IF Noise Problem!

Gentlement, I need some help: My R390A has a noise problem in the first IF amp
stage that I'm having trouble locating. It produces a popping, crackling noise
when things warm up a bit. Sometimes it comes and goes, but it seems to be
getting worse. It sometimes breaks into an almost continuous crashing noise
then later might settle out to occasional pops or hisses or dissappear for a short
time. I isolated the problem by pulling the input cables from the RF deck - no
change. Pulled V501 and all is quiet. Back in, noise returns. I've checked resistor
values and they seem within range (all high as usual).

I've recapped C504, C505, and C553. I've swapped the V501 with several other >
tubes with no joy. The noise is affected by the bandwith control only in its
frequency response. At narrower bandwidths, the popping still occurs, just low
amplitude lower frequency components of the noise. I've tried freeze spray on
the components in the area (and everywhere else) with no change in the noise.
IF deck tips                                     page 57

Does anyone have a suggestion? Should I start replacing resistors? Can the mica
caps cause symptoms like this? What components should I focus on first? Has
anyone else experienced a problem like this? I appreciate your help in advance.
Well, I've now replaced all of the resistors and all but C50 and C503 around the
1st IF stage, and the noise is still there! It comes and goes at will. I've re-soldered
all of the connections in the area that I can. I'm running out of ideas. Can anyone
offer a debugging suggestion? Could it be in a different stage? As noted above,
the noise is present without a connection to the RF input. The noise goes away if
I remove V501.

The sound of the noise gets filtered by the BW filters but does not go away. With
the 'scope I can definitly see the noise bursts on the plate of V501, but can't see
anything on any other pin (my scope probably doesn't have enough sensitivity).
Could it somehow be Z501? If so, what should I try?
Date: Sat, 17 Mar 2001 18:49:11 -0700
From: "Kurt" <radiouser@uswest.net>
Subject: Re: [R-390] Re: IF Noise Problem!

The noise that you describe can be made by a bad mica cap. The thunder storm
sound is fairly well documented in the Hollow State News Letter with it's cause
traced to bad micas. Using a can of freeze spray you can isolate the bad cap or
you can just replace them all around V-501.

Everyone worries about replacing all of the paper caps because they leak. I have
had just as many problems with the postage stamp micas; especially the pink
ones with only the color code for the value. When testing / replacing the micas
don't forget the ones that are part of the 0.1kc -1kc crystal filter. Even though
they may be out of the circuit they can still make noise.
Date: Sat, 17 Mar 2001 20:29:48 -0800
From: "khgrant@ix.netcom.com" <khgrant@ix.netcom.com>
Subject: Re: [R-390] Re: IF Noise Problem!

Thanks for the tip on the caps. I have not replaced any of the micas yet. I tried
the freeze spray and couldn't alter the symptoms at all. What kind of cap is inside
of Z501? It is one of those short hollow tubes with the leads wrapped around on
each end. Is that a mica cap? Looks like I'll need to find some replacement caps
for the filter circuit. What type of caps should I use to replace them with?
Date: Sun, 18 Mar 2001 00:13:00 -0500
From: "Tetrode" <tetrode@sprynet.com>
Subject: Re: [R-390] Re: IF Noise Problem!

Keith, as another idea, don't forget the tube socket itself as a source of noise
problems. I've got one in the RF deck that occasionally gets noisy despite careful
cleaning and application of dexoit. The noise was independent of the tube put in,
and only went away after a treatment. Next time I go through the radio I plan to
get a very small wire brush and polish the socket contacts.
IF deck tips                                      page 58

Date: Sun, 18 Mar 2001 18:37:56 -0800
From: "khgrant@ix.netcom.com" <khgrant@ix.netcom.com>
Subject: Re: [R-390] Re: IF Noise Problem!

Well, this is turning out to be a saga! I thought I had the noise isolated to the first
IF stage, but I was wrong. I replaced almost all of the components around V501,
but the noise kept comming back. Then I tried pulling V501 again just to be sure
and the popping / crackling noise came back after warm-up. Thanks for all of
the suggestions from the group so far. I checked the socket pins for V503 and
they seem to make good contact.

Here is an interesting experiment I tried: I disconnected V502 pin 1 (the input to
the 2nd IF amp coming from the BW filters) and connected it via a new 22k
resistor to the AGC line, isolating the 2nd IF from the first IF. With this setup, the
nose returned. However if I bypass pin 1 to ground with a 0.005 uf cap, the noise
goes away! Why would this happen? I tried using the bypass cap on pins 2 and 6
with no affect.

I'm beginning to wonder if I'm getting noise coupling in from some other stage.
Someone suggested that the mica caps in the mechanical filter section might be
the cause, but I don't see how that could be the case when the noise is present
with the 2nd IF disconnected from the filters. Has anyone seen disk ceramics
produce this type of popping crackling noise? I'm still searching for the problem.
Anyone have ideas I can try?
Date: Mon, 19 Mar 2001 18:13:46 -0700
From: "Kurt" <radiouser@uswest.net>
Subject: Re: Re: [R-390] Re: IF Noise Problem!

Keith: Perhaps you have a bad silver mica somewhere along the AGC line.
Remove the jumper on the back of the radio between TB102 terminals 3 and 4.
This will separate the AGC line in the IF deck from the AGC line in the RF deck.
There are several silver micas along the agc line in both the IF and RF decks.
Date: Wed, 21 Mar 2001 18:40:07 -0800
From: "khgrant@ix.netcom.com" <khgrant@ix.netcom.com>
Subject: [R-390] Re: IF Noise Problem (continued)

[an ongoing saga continues...Well, thanks for all the help so far on the noise
problem in the 2nd IF stage.

Here is where I am: the 1st IF amp has been removed (V501), and the 4th IF amp
has been removed. The AGC has been disconnected at the rear. Power supply
looks good. No other oscillations in other parts of the IF. I have replaced all of
the components around V502 and V503 except for a couple of ceramic 0.005 caps
and R514 and R550. I also replaced R511, the resistor across the input of T501. I
monitor the noise on the plate of V503. With my 'scope, I
IF deck tips                                      page 59

think I can see the noise on the plate of V502, but it is hard to tell. At this point,
my best guess is that the noise is coming from the plate circuit of V502. Based on
a process of elimination, that pretty much leaves the mica cap across the input to
T501 (C557).

A puzzlement: I can kill the noise by hooking a 0.005 uf disk between the grid of
V502 and ground. Why is this? My knowlege of tube operation is somewhat
limited. The noise is NOT coming from the filter section (I disconnected V502
from that).

Question: I know these caps were selected at the time the IF transformer was
built. How badly will I screw up the performance of the transformer if I replace
it? Does anyone have a (good) replacement for T501?

Any words of wisdom (or encouragement)? Thanks for putting up with my
Date: Wed, 21 Mar 2001 20:04:40 -0800
From: "khgrant@ix.netcom.com" <khgrant@ix.netcom.com>
Subject: [R-390] IF Transformer Question

I have a question about the T501 IF transformer in my R390A.

I suspect that the mica cap across the primary may be the source of noise in my
radio (I've done a lot of work trying to isolate it). I looks like there are actually 2
caps across both the primary and secondary windings. One on each side is a mica
cap near the top of the can. The others are down near the bottom next to the
resistors. They have a shape somewhat like a 1/2 W resistor, but the leads are
radial and the body is rounded like it was dipped in a coating. Anybody know
what kind of caps these are? How about the color code they use? They seem to
have colored dots (blobs?) along one side.

If you were to guess which cap (on the primary) might be going bad on me,
which one would you guess? Others on the list have mentioned silver-micas
going bad on them, so I am wondering about this other cap in the transformer.

I'm a little nervous about replacing compenents in the transformer. I don't want
to screw up its Q. Anyone rebuilt an IF transformer before?
Date: Thu, 22 Mar 2001 09:09:13 -0800
From: "Roger L Ruszkowski" <rlruszkowski@west.raytheon.com>
Subject: [R-390] [R-390A] IF Transformer Question

I have a questions about the T501 IF transformer in my R390A. I suspect that the
mica cap across the primary may be the source of noise in my radio (I've done a
lot of work trying to isolate it). There are actually 2 caps in the transformer
cans. One is across the primary winding and a second one across secondary
windings. Some caps are near the top of the can. The others caps are down near
the bottom next to the resistors. Some caps in my receiver have a shape
IF deck tips                           page 60

somewhat like a 1/2 W resistor, but the leads are radial and the body is rounded
like it was dipped in a coating. They seem to have colored dots (blobs?) along
one side. Anybody know what kind of caps these are? [1950's style mil spec
caps!! Silver on mica with a round body cover. Silver on ceramic with a hollow

How about the color code they use? Compare your part to the TM and you can
determine the pattern from end to end. The dot are like the color bands on the
black beauties caps. The Radio Armature hand book has a page on how to read
the dots and bands. Some web pages are also available if you are endowed with
net access]

We know the caps in the IF transformer were selected at the time the IF
transformer was built. How badly will I screw up the performance of the
transformer if I replace the caps?

[No problem, The slug will let you tune the circuit back to the correct frequency.
If the slug goes to center and does not peak then you need more cap. If the slug
drops out the end and does not peak then you need less cap. More or less cap
here being a fraction of PF.]

Others on the list have mentioned silver-micas going bad on them, so I am
wondering about these caps in the transformer can. If you were to guess which
cap (on the primary) might be going bad on me, which one would you guess?

[If you have more than one cap on the side of a transformer, these are just two
parts to get the selected design value. Silver mica caps do go bad. But at the low
failure rate, predicting if its this one or that one based on collective knowledge is
still pretty vague at this time for the circuit under consideration here.]

>I'm a little nervous about replacing components in the transformer. I don't
want to screw up its >Q. Any words of wisdom (or encouragement)? Anyone
rebuilt an IF transformer before?

[Been there, done that. The cans have a cover, off with the cover. Inside is a top
board and a bottom board. Two studs space the boards apart, hold the cover on,
mount the can to the deck and frame the stack. Ignore these. On one side of the
stack will be a pair of wires from board to board (up and down in the stack).
These extend through the bottom board and are the "lugs" for the "transformer".
On the other side of the stack is the same setup. One side is primary. The other
side is secondary. The coil, cap, (caps), resistor, (resistors) tie between a pair of
these stack wires. Past experience has been cold solder joints. Some very fine skill
and things in there can be fixed. In the process of working on the lugs under the
can, heat moves up the wires and melts joints in the stack. If you replaced any
caps under the deck to one of these can lugs, you may have a cold solder joint on
the wire in the can above the lug you needed to work on. The cap or two I seen
go bad, were broke and were replaced. We ordered a new can to get the cap and
changed the cap in the can rather than changing the whole can from under the
deck. We put the new can cover on the stack and dropped the rest in the trash. A
IF deck tips                                      page 61

50 year old bad mica is likely, I myself am trying to locate the one (or more) in
my IF deck Doing a cap swap in the stack is a low risk venture and you should
give it a try. After you do the work in the stack, go back to the bottom and check
the "lugs" for cold solder joints there. The "Cans" are robust circuits and at
455Khz you are OK. Work in the stack will not trash the Q or get you so far out
of value that you can not tune the transformer to a proper peak.]

>Does anyone have a (good) replacement for T501? Maybe just the right value
caps? Thanks, Keith                       [Good Luck with this problem Keith, Do let us
know what you find.]
Date: Thu, 22 Mar 2001 21:56:20 -0800
From: "khgrant@ix.netcom.com" <khgrant@ix.netcom.com>
Subject: Re: [R-390] Re: IF Noise Problem (continued)

Thanks for the tip on re-soldering the leads. When I get back to the bench,I'm
going to try resoldering all of the circuit connections. Failing that, I'll pull out the
cap and replace it. Appreciate the help! Keith
Date: Thu, 22 Mar 2001 21:57:50 -0800
From: "khgrant@ix.netcom.com" <khgrant@ix.netcom.com>
Subject: Re: [R-390] [R-390A] IF Transformer Question

Thanks Roger, I'll give it a go! Keith
Date: Fri, 23 Mar 2001 20:56:42 -0800
From: "khgrant@ix.netcom.com" <khgrant@ix.netcom.com>
Subject: [R-390] [IF noise problem] Cap color code?

Well, I've resoldered all of the connections around V502 and V503, including the
internal connections of the IF transformer with no success. I replaced one of the
caps across the input side of the IF transformer. It was a silver-mica. No success.
What I am left with is a second cap across that input, and thus the question about
the color code. I know what the colors are (bad booze rots....etc). I need to know
how to interpret the meaning of the numbers.

I have a small cap from my IF transformer, about the same size and shape as a
1/2 watt resistor but with rounded ends, like it was dipped in epoxy. The leads
come off radially, not axially like a resistor. The colored dots start near one end.
Which way do I start reading, and what
do the digits represent?
Date: Sat, 24 Mar 2001 21:38:27 -0800
From: "khgrant@ix.netcom.com" <khgrant@ix.netcom.com>
Subject: Re: [R-390] [IF noise problem] Cap color code?

[I'm not sure I sent message properly, so I am sending it again. Sorry if it get's
duplicated] Ok, I need help with the color code of this small cap I pulled out of
my IF can. It is a small radial with a brown body. It has a large violet spot on one
IF deck tips                                      page 62

end, followed by smaller orange, white, black, and red dots. Now I don't know
which dirction to read the digits so it is either:
†††††††† 7 3 9 0 2 † or † 2 0 9 3 7 I'm sure at least one of the digits is a tolerance
value? I'm guessing that this should be small value cap. Maybe 39pf or 200pf?.
Could someone help me out with this one?
Date: Sun, 25 Mar 2001 17:47:20 -0800
From: "khgrant@ix.netcom.com" <khgrant@ix.netcom.com>
Subject: Re: [R-390] [IF noise problem] Cap color code?

> According to the information I have I offer the following. The cap appears
> to be a Group III Temperature Compensating Style CC Capacitor.
> The large violet dot is the Temperature coefficent and for your application
> (violet) -750 parts per million per degree centigrade.
> Orange dot is the 1st significant figure...3
> White dot is second significant figure....9
> Black dot is the Multiplier......1
> Red dot is the capacitance tolerance =/- 2% given you are over 10 uuf in
> value.
> Hope this helps. By the way is there a yellow MIL identifier dot on the
> rear of the cap?
> Duffy (N3JHA)
Date: Sat, 7 Apr 2001 16:20:32 EDT
From: Llgpt@aol.com
Subject: Re: [R-390] BFO

>To answer a few who saw I was not clear,- the BFO just sits there for 45 sec. to a
min.,, then it >starts doing it's thing...Tube o.k., Circuit checked o.k. when the
deck was re->capped..(Actually, I mean that long after the radio is warmed up
and recieving..)

Try this, I had this happen a few years ago to me. The BFO front panel switch
was dirty. Clean with de-oxit or your choice of cleaners then try it.
Date: Sat, 7 Apr 2001 19:52:33 -0400
From: "Tetrode" <tetrode@sprynet.com>
Subject: Re: [R-390] BFO

I've got a pretty good idea what's going on with your radio, although it's not a
big deal. In both the 390A and nonA the BFO and VFO tube filaments are in
series and their filament current is derived from the infamous 3TF7 ballast tube.

I once had the same problem you do with one of my nonA's except that it was
the VFO that took a while to start up, and sometimes it wouldn't even want to
IF deck tips                                     page 63

start unless the line voltage was a few volts on the high side. The problem was
the ballast tube was only delivering about 10 VAC to the filament string instead
of the nominal 12.6 VAC, so the VFO tube's cathode emission was reduced and
the oscillator had a hard time starting. For a short term fix I put in a fresh VFO
tube that had more emission and wasn't bothered by the low filament current,
but later I did the usual mod to the ballast tube socket so that I could substitute a
12BH7 and things have been fine since.

Out of six 3TF7 tubes I have only two have an output current that is within 10%
of their 300 mA spec, which is supposed to supply a nominal 12.6 VAC output in
this particular application. The other two were well below, and two were well
above. I would guess not many folks bother to check their ballast tubes and just
assume that if they aren't open they are OK. However, my experience tells me
they can degrade over time just like any other component, or maybe they were
never quite good to start with (rejects?).
Date: Mon, 16 Apr 2001 09:57:00 -0600
From: Jordan Arndt <jordana@nucleus.com>
Subject: Re: [R-390] IF Noise Problem

I have just found a contributor to this type of noise.. it has been a problem in my
SW for awhile now, and I have discovered it coming from the PTO... it occurs
together with a slight shift in frequency of the PTO output, and can be heard as a
slight audio shift through the passband in AM mode or a shift in Het frequency
with the BFO on.... This may help in your case also... 73 de Jordan....
Date: Mon, 16 Apr 2001 13:22:08 -0500
From: Roy Morgan <roy.morgan@nist.gov>
Subject: Re: [R-390] IF Noise Problem

Disk ceramics, as with everything else, can fail and have done so. Use your
oscilloscope to see if the one of the caps is causing the trouble. Bypass any
suspected cap with a MUCH BIGGER one.. if the noise gets less, you have found
the culprit.. Use of a socket extender helps a LOT here.. if none available, hook
the new BIG bypass cap directly to the pins of a tube (insulate with teflon
sleeving to get it into the tube shield base with out shorting) and see what

SOME few socket extenders have little cotter pins on each tube pin allowing you
to unhook each one. If you have such an extender, you can isloate the suspected
screen, say, with its cap and feed it externally with another dropping resistor and
cap. Take heart.. if you have replaced ALMOST everything, you are almost there!
IF deck tips                                      page 64

Date: Mon, 16 Apr 2001 22:04:43 -0400
From: Jim Miller <jamesmiller20@worldnet.att.net>
Subject: Re: [R-390] IF Noise Problem

I would also check resistors, especially screen, plate and cathode resistors. They
can break down with age. I changed out about 100% of the 2200 ohm resistors in
my IF strip because they had drifted out of tolerance. A cracked resistor could
cause noise like that. And from experience I know you can have one that is bad
internally and look perfect externally. Maybe some cooling spray would reveal
something. N4BE
Date: Mon, 23 Apr 2001 11:03:06 -0400
From: "Chuck Rippel" <avsl@erols.com>
Subject: Re: [R-390] Harmonic Crystal Help Needed

Bad crystals are not uncommon. That problem typically mainfests itself as bands
that are "out" or large frequency differences when changing from band to band.

First, make sure the rear panel "OVENS" switch is off (turned full to the left stop).
That should not be on unless you happen to have the radio out in the arctic cold.

Failing that, go to International Crystal and simply replace all of the crystals.
They are about $20 each. typically, the know what crystal type is needed once
you tell them what radio it goes in. However, should they not, ask them for a
type CR-36/U which is in an HC6/U configuration..

I would also replace the 17mhz 1st crystal oscillator and also 200khz calibrator
crystal while you are at it.

They have several grades of crystal, I would ask for the mid-grade.

Their number is (800) 322-9426
- -------------------------------------------------------------------------------------------------------
Date: Mon, 23 Apr 2001 08:57:40 -0700
From: "Roger L Ruszkowski" <rlruszkowski@west.raytheon.com>
Subject: [R-390] BFO micro dial

Yes, Kevin, Micro Dials are available and you can add one to any 1/4" shaft you
may have. The dials were an ASA modification for better BFO set up. These were
used on receivers dedicated to RTTY copy. The dials count up or down. and will
turn until they roll over. On the receiver there is no stop. You can crank your
BFO or BFO coupler right into the trash with one of these dials. A count of about
11 is 1Khz. so +033 is +3Kz and 977 is - -3Khz. You can go to about + or - 4Khz if
you have your coupler well adjusted so you do not over stretch or of squish it.
The BFO coil unit will provide that range on both sides of 455Khz.

I use to know the numbers for setting the counter to different RTTY shifts. The
micro dial numbers were easier to tune up than the original knob. For CW work
IF deck tips                                      page 65

its a wash. For SSB it helps. It is a bolt on change. You change the knob and the
front panel bushing. You need the very small allen wrench for the knob set
screws. Once you get it assembled right, you can drop the IF deck in and out
with no more effort than with the standard knob.

Any bolt on geared knob would function as well. The micro dials just looks as
cool. Ay mon it's was a spook receiver in its last life.
Date: Mon, 23 Apr 2001 11:04:08 -0500
From: "Scott, Barry (Clyde B)" <cbscott@ingr.com>
Subject: RE: [R-390] Harmonic Crystal Help Needed

You might want to buy an entire crystal deck from ATC (www.atc.com). While
the deck itself is pretty much trashed, it comes with a full set of crystals. Bear in
mind, though, that they aren't guaranteed to work either, but it might be worth
it to have the spares on hand. They're only $27 now. Note this doesn't cover the
17mc or 200kc crystals.
Date: Mon, 23 Apr 2001 15:49:45 -0700
From: K7JB John <k7jb@uswest.net>
Subject: Re: [R-390] Harmonic Crystal Help Needed

I took a look at the crystal deck enlarged photos from ATC and looks like about
all you get is the crystals. The ceramic adjustment caps are all missing, so those
of you who think you are getting a full drop in deck, look again! Good price for
crystals if they work. I have a deck I got from Fair Radio with crystals and have
often wondered if the small red mica caps in parallel with the ceramic adjustment
caps might suffer from silver migration. I found plenty of them in my 75A-4 that
were either leaky or just plan shorted which results in all kinds of noise
problems. If they were leaky in this crystal deck, makes me wonder how much
the output of the oscillator would be down in signal amplitude, or just dead! If
anyone has replaced any of these and noticed that the signal amplitude has come
back up, it would be nice to hear from you. Anyone been there, done that?
Date: Mon, 23 Apr 2001 20:50:35 -0500
From: Tom Norris <badger@telalink.net>
Subject: [R-390] Crystal Help Needed

This is not aimed at anyone in particular, just those that fuss about ATC and
mark's posts and products. This is NOT meant as a personal attack on the folks
doing the fussing, just a commentary on my part so take it as you will. ATC is
advertising the deck as a source of crystals only and is pretty specific in letting
you know that is what you are getting. I have one. The crystals are brand new,
and all are on frequency, much more than the ones in the receivers I have
currently. I may try to purchase another deck if there are any left. At $10 per
crystal at Fair and others, this complete set is a steal!!!
IF deck tips                                      page 66

There are very few folks left that even sell surplus of any kind as it is usually
cheaper to just toss it in a landfill. Mark is doing the R-390 and GRC-106
community a SERVICE by offering this stuff.

Why do folks continue to criticize him for helping us? Much more of the
demonizing, and HE will start putting the few parts he has left in the dumpster
along with the lions share that went in there to begin with. The stuff on the web
site is just a fraction of what was there before the dumpsters were filled. ATC
was a major subcontractor on the 390A and the GRC-106 and other items. ( My
1967 EAC unit has all ATC coils for instance! )

He is doing up a favor for Pete's sake!
Date: Mon, 23 Apr 2001 22:09:28 EDT
From: Llgpt@aol.com
Subject: Re: [R-390] Crystal Help Needed

My.002 cents worth, Tom I agree with you 100%. There will always be the
bitchers and grumblers no matter what is being sold. I can remember when
Chuck sold the spare tube sets along with a bunch of "extras" and people bitched.
Well folks guess what........ There will be less of it tomorrow than there is today.
Get it while you can.
Date: Mon, 23 Apr 2001 21:25:22 -0500
From: "Bill Hawkins" <bill@iaxs.net>
Subject: RE: [R-390] Crystal Help Needed

This could only be said by someone who does not care about the money. And so
it is with the people who complain about ATC. They do not understand what is
being offered. I can only hope that Mark is encouraged by the money that rolls
in, and not discouraged by words that would not be uttered where the buffalo
roam. (and the skies are not cloudy all day ...)
Date: Tue, 24 Apr 2001 12:29:30 -0400
From: "Chuck Rippel" <avsl@erols.com>
Subject: Re: [R-390] Crystal Help Needed

I have met Mark personally and can tell you he is very helpful and was very
reasonable to deal with. Anyone should have no problem getting something he
has but, selling R390A parts to individuals is not ATC's main business thrust. Its
something they are doing to make a few $$ on the inventory they still have. I
explained to Mark the following the radio has and he is accommodating we
R390A owners by NOT throwing the spares he has in the dumpster. Be patient
with him. He's trying to help. Just because one might not get the
answer you want to hear does not mean they or their company are bad.
IF deck tips                                      page 67

Date: Tue, 24 Apr 2001 23:09:47 -0400
From: Jim Miller <JamesMiller20@worldnet.att.net>
Subject: Re: [R-390] American Trans-Coil

ATC has a selection of trimmers that are in the form of multiple trimmers on a
single phenolic board intended for use in various coils and IF cans. The board
sizes he has aren't directly compatible with the trimmer boards in the xtal osc
deck. However, I have repaired bad trimmers in the xtal deck individually by
disassembling the trimmer. You can remove the rotary part and the dielectric
pad, then replace the pad and rotor with the same parts removed from a good
trimmer. To disassemble a trimmer is very simple. Just use needle nose pliers to
gently pull the retaining spring metal on the reverse side...slide it away from the
shaft. Works like a champ. Getting to the trimmer boards in the xtal deck is a
little tedious, requiring desoldering of a coupld of wires, removal of the switch
shaft, etc. But it can be done. Never ever get deoxit or other chemicals on the
trimmer parts, however. Jim N4BE
Date: Wed, 25 Apr 2001 10:16:52 -0400
From: "Chuck Rippel" <avsl@erols.com>
Subject: [R-390] Re: American Trans-Coil

I have literally thousands of Erie Trimmers for the R390A brand new, still sealed
in the bag.
Date: Thu, 26 Apr 2001 21:10:35 -0400
From: Bob Camp <bob@cq.nu>
Subject: [R-390] Interesting Crystals

I was tearing into the crystal oscillator deck on an R-390A and came across an
interesting problem. Every crystal in the deck had vented. I *assume*this
happened after the radio went in service and they were not manufactured with
an open hole out to atmosphere. Am I correct in guessing that the oven heaters
must have run away to make this happen ? If they did they sure didn't damage
much of anything else. Obviously the fix is to heat up the crystals and re-seal the
vent hole when they are hot. The question being has anybody else tried this and
had any luck with the process. Normally an HC-6 gets sealed right after
calibration. They aren't designed to see atmosphere for long ...
Date: Thu, 26 Apr 2001 22:30:37 -0400
From: "Charles A./Leonor L. Taylor" <calltaylor@earthlink.net>
Subject: Re: [R-390] Interesting Crystals

Go ahead and solder-seal the crystals. I won't tell anyone if you won't. If they
don't work, recycle them into an environmentally acceptable container such as a
dead hippy. Crystals are evacuated (something your mother spanked you for
doing when you were young) and repressurized with some sort of inert gas
[argon, pluton, klingon, whatever] to prevent oxidation of the elements.
IF deck tips                                      page 68

Date: Thu, 26 Apr 2001 22:47:34 -0400
From: Bob Camp <bob@cq.nu>
Subject: Re: [R-390] Interesting Crystals

Actually the HC-6 stuff never made it to the evacuation / back fill process. At
least not in any of the crystal plants I've worked in. Back fill and all that stuff
came along with resistance weld or was a coldweld / glass type process. The
solder seal process just ran them down a heat track that melted the solder at the
base. They slid down the track and cooled off enough to let
the seal harden. Then the girl hit the vent hole with a little solder to seal the can.
They were good and hot at the time but not back filled.

The only exception to this that I am aware of was a process they used in
Germany on and off over the years. They would blow a little iodine into the part
just before seal. The idea being that it would act as a getter. From what I've seen
it didn't work very well ....

Still seems pretty weird that the crystal oven could get hot enough to do that to
the crystals ....
Date: Tue, 1 May 2001 15:44:18 -0400
From: "Chuck Rippel" <win.308@home.com>
Subject: [R-390] Significant R390A WWW Site Updater

I just added a significant section to the R390A WWW Site. New is a full overview
of the various IF filters used in the R390A. I think the results will suprise you!

Go to: http://www.avslvb.com/R390A/index.html Look next to the "New"
symbol and click on the "About R390A Filters" link. That will take you to a direct
link to the story also acessible from the "New Additions" page.
Date: Tue, 22 May 2001 10:17:11 -0500
From: Roy Morgan <roy.morgan@nist.gov>
Subject: Re: [R-390] Son of a Question For The Assembled Multitude

>Well I did a little more fiddling with my T-501 core problem.
>3) Find another T-501 - anybody got one ?

If you get to that point, do let me know.. I just might have something here..

>I doubt that the coil is causing that big a problem, but the IF does peak up
>better if I drop a lump of ferrite on a stick into the core.

BINGO! Find a small core that fits the thing, slice off a short section, and put it in
there to improve the adjustment. WAX it and the tube before you do and you'll
have no further sticking problems. (Use butchers wax or car wax.)
IF deck tips                                      page 69

Date: Fri, 13 Jul 2001 13:47:36 -0700
From: "Roger L Ruszkowski" <rlruszkowski@west.raytheon.com>
Subject: Re: [R-390] R390A rebroadcaster

<snip>..........how to run an IF deck while out of the radio... <snip>

Set the R390 up on end, on the bench. The IF deck will then set on the bench and
can be plugged in and operated. You can give it a quarter twist so you can peak
into the under side. You can also put the If deck up on blocks so you can have a
bit more cable freedom. You do have blocks for your R390 service bench don't
you? Would you set be natural wood? or the custom stained ones?

P.S. Why do you think its your work that has this receiver broadcasting in the
FM Band? It could have a bug in there. I could have a mod to relay some
shortwave stations to the local campus. You may own a repeater and just not
understand it yet. Then again !!! Do let us know what you find.
Date: Fri, 13 Jul 2001 17:57:56 -0400
From: Roy Morgan <roy.morgan@nist.gov>
Subject: Re: [R-390] R390A rebroadcaster

I seem to remember one field change for the R-390 that was to cure "spurious
oscillations". You should investigate all known field changes and see if there is
one related to this symptom.
Date: Fri, 13 Jul 2001 15:59:50 -0700
From: Richard.McClung@dielectric.spx.com
Subject: Re: [R-390] R390A rebroadcaster

This may or may not help. Short version..........................
                    Department of the Army Modification
                    Work Order
                    MWO 11-5820-294-35/2 Modification of
                    the Radio Receivers R-390/URR and
                   R-390A/URR to Eliminate Spurious
                    5 October 1959

                            Purpose of modification is to
                            eliminate continious radiation at
                            340 mc as a result of parasitic
                            oscillations, by connecting the
                            suppressor grid to the
                            cathode of the local audio output
                            tube V603.
IF deck tips                                      page 70

                            Unsolder and remove the jumper lead
                            connected between pin 2 and fround
                            of tube socket XV603. Connect and
                            solder a suitable length of No. 22
                            AWG solid wire between pins 2
                            and 7 of tube socket XV603.

                            Unsolder and remove the jumper lead
                            connected between pins 2 and 4 of
                            tube socket XV603. Connect and
                            solder a suitable length of No. 22
                            AWG solid wire between pins 2 and 7
                            of tube socket XV603.

Date: Fri, 13 Jul 2001 16:12:38 -0700
From: "Roger L Ruszkowski" <rlruszkowski@west.raytheon.com>
Subject: Re: [R-390] R390A rebroadcaster

>I seem to remember one field change for the R-390 that was to cure "spurious
oscillations". You >should investigate all known field changes and see if there is
one related to this symptom........ Roy

Great Thought. Let's get those details up here again folks. Wallace needs some
help here. My humor on bugs is the answer he needs. One of those spurious
oscillators is getting him for sure. What luck to have it hit the FM band and
actually know the problem exist. How many of us have our own radiating decks
and do not even suspect it? Roger.
Date: Sat, 14 Jul 2001 09:35:27 -0400
From: Bob Camp <bob@cq.nu>
Subject: Re: [R-390] R390A rebroadcaster

The first question : "is this a bug or is it a feature ? ". People go to great lengths
to improve the audio chain of R-390's and running them through an FM stereo
system sounds like a good idea who's time has come :) Time to box it up and sell
it on eBay for *major* bucks.

First thing to try is to turn the RF gain all the way down. An easy way to do that
is to pull the jumper on TB102 that's between pins one and two. That kills V501
and V502. The audio on the carrier will go away when you do this. The thing to
watch is weather it kills the carrier. If it kills the carrier then I'd bet on something
wrong with one of those two tubes.

Next try the good old pull the tubes trick (pull a tube put it back in, pull the next
one ...). See if when it stops. If you are lucky it will only stop when you pull one
of the tubes. Start with the AGC and detector tubes (V506 / V509) and work
IF deck tips                                     page 71

back towards the first IF amp tube. As you pull each tube out check the
markings to see if some previous owner "improved" things by making a tube
substitution. The 6BA6 isn't a super hot tube and people have been known to put
in "better" tubes. Generally the result is a mess (like maybe VHF oscillation ...). If
you come across any that are from countries that you need a visa and shots to
visit you might sub them temporarily .... Next I'd check the connections on the
new capacitors you put in. A lot of what you do a re-cap job is to replace screen
bypass caps. If you get one wrong, or if it's defective you can get VHF
oscillation. I still find it *very* hard to believe that anything the size of those
clunkers does any good at all at VHF but that's what the book says.

If you have seven pin and nine pin tube socket extenders I would at least try
them. With parasitic oscillations they may not help since the oscillation may go
away with the culprit tube up on the extender. If not you should come across a
tube with a lot of 98 MHz on it's plate or screen. Usually it's volts peak to peak,
not milivolts that you are looking for.

Once you identify the tube that's doing it then flip the deck over and visually
check a couple of things. There should be a short from the suppressor grid to
cathode or to ground. Plate, screen, and cathode bypass caps are next. If they all
look ok then start poking around on the IF deck live. Paralleling bypasses is
probably the first step. Hope this helps. Some of it is fairly basic - sorry if I went
back to far.
Date: Sat, 14 Jul 2001 11:26:45 -0400
From: Bob Camp <bob@cq.nu>
Subject: Re: [R-390] R390A rebroadcaster

Tubes are very high frequency devices. The lead dress in a 390 is not the sort of
thing you would do at 100 or 300 MHz. Any time you significantly move parts
around in one of these radios you may start things going. I have not checked my
radios for this sort of thing. Probably the easiest way to check would be a sniffer
loop on the end of a piece of coax. Plug the other end into a spectrum analyzer
and you could spot the problem pretty quick. Fixing the problem once you
spotted it would take a bit more time. I suspect that the problem is more likely to
happen in radios that have major mods or weird tubes. Obviously the military
ran these radios for a long time with very few problems. There's nothing in the
TM's about checking for parasitic oscillation. If the 390's routinely sing at VHF I
suspect that they would have found it to be a problem for them. They had
enough stuff running up there that it would have messed them up big time.
They certainly found the audio stage oscillation problem and sent out a mod to
fix it.
IF deck tips                                      page 72

Date: Mon, 16 Jul 2001 17:32:44 -0700
From: "Wallace Gibbons" <rockwall@sourceoneinternet.com>
Subject: [R-390] R-390A Rebroadcaster update

I spent a little time chasing the FM broadcast capabilities of my R-390A last night.
I traced to the offending stage with a FM receiver with an S meter and a small
coupling loop connected to the antenna input. I poked around the IF deck (and
audio, just in case) and looked for the strongest signal on the FM receiver. It's the
6AK6 IF stage that's the culprit. I pulled the tube prior to that stage to stop the
455 khz IF signal. Then I plugged in a 7 pin tube test adapter to give me access to
the 6AK6 pin signals on the top of the chassis, and with a scope I could see the
oscillation on the plate, screen, cathode, of the offending stage. The measured
frequency was about 102 mhz. I tried better high frequency bypass caps on the
cathode and screen to ground. No help at all. The only way I could stop the
oscillation was to turn the BFO neutralizing trimer cap (C525) until the oscillation

Judging from the circuit used for that BFO neutralization cap, and the feedback
path it takes off the plate winding of the 6AK6, well, looks like it could be
positive feedback with some parasitic circuit inductance and the right trimmer

I don't use the BFO on this receiver so I set the trimmer for the middle of the
tuning range where the stage doesn't oscillate, and that appears to have got rid
of the offending oscillation. The oscilloscope doesn't show any signal at all on the
plate unless the prior stage tube is replaced back in it socket.

Just thought I'd pass this along, I'd be interested in comments about the
oscillation and the reasons for it. Maybe the IF gain is set to high?

The oscillation is gone, receiver seems to be working fine, I don't use the BFO so
can't comment on my repairs effect on that. Maybe this winter I'll dig deeper, for
now it's OK.

Thanks to all on the list who emailed comments and suggestions.
IF deck tips                                      page 73

Date: Tue, 17 Jul 2001 00:29:51 -0400
From: Norman Ryan <nryan@intrex.net>
Subject: Re: [R-390] R-390A Rebroadcaster update

Nice work resolving the oscillation problem. It will be nice to learn more about
its why and how sometime. Here is a simple procedure for setting IF gain,
developed by Chuck Rippel.

Setting IF Gain on the R-390A:

1. Disconnect antenna.

2. Tune to 15.2 MHz.


4. Set BANDWIDTH at 4 KHz.

5. Set RF GAIN at maximum.

6. Peak ANT TRIM.

7. Set LINE METER at -10 DB scale.

8. Set LINE GAIN at maximum.

9. Adjust IF GAIN ADJ (R519) for LINE LEVEL meter reading
   between -4 and -7 DB.

10. Re-zero CARRIER METER with CARR METER ADJ (R523).

Re-zeroing Carrier Meter:


2. Set RF GAIN at minimum.

3. Adjust CARR METER ADJ (R523) for zero setting on carrier level meter.
Date: Tue, 17 Jul 2001 10:36:09 -0400
From: "AI2Q Alex" <ai2q@adelphia.net>
Subject: [R-390] Quashing VHF oscillations

Now that you've localized the 102 MHz re-radiation problem, why not try using
some judiciously placed ferrite beads at the offending IF stage? Slipping a bead
or two over the grid pin, or even possibly the plate and/or screen pins, won't
affect normal operation one iota, but may very well add enough series
inductance to quash the parasitic circuit.
IF deck tips                                 page 74

In fact, being as the oscillation seems resistant to the tube adapter (did you see a
change of frequency at all when you inserted the adapter?) you might be able to
make a "chicken connection" of the ferrite beads on the adapter, just to see if they
affect the oscillation.

If you think you're on track, you might think about winding some small parasitic
suppressors as an alternative to beads. Use a few turns of wire over a 47-ohm (or
so) carbon resistor (putting the coil and resistor in parallel). That forms a low-Q
lossy element that may stop the oscillation.

You could try putting one in series with the control grid, and/or the plate lead.
I've used these successfully in RF amplifiers to prevent (not stop) parasitic
oscillation. In those circuits I can "see" the VHF resonant frequency with my grid-
dip meter, and then de-Q it with the loaded
suppressor resistor-coil combinations.
Date: Mon, 23 Jul 2001 22:31:38 -0400
From: "Walter Wilson" <wewilson@knology.net>
Subject: [R-390] Popping noise with the BFO on

I've been chasing a problem for several weeks, which just about has me
whipped. It's a popping noise (like popcorn in the microwave) after I turn the
BFO on. Here are the symptoms: It happens with any IF deck installed in this
chassis. Move the IF deck to another chassis, and it works fine. Same situation
for the AF deck, Power Supply, PTO, and RF deck. The problem always stays
with the chassis (I've verified this twice). So I've concluded the problem has to
be somewhere in the chassis wiring or the chassis-mounted components.

The noise seems to start in the detector stage. If you pull V504, the noise is still
present. If you lift the BFO injection lead (12 pF coupling capacitor), the noise of
course disappears; just like turning the BFO off with the switch. I thought it
might be a bad BFO switch or bad wiring to the switch, so I jumpered around the
switch inside the IF deck. No change. I also jumpered the diode load inside the
IF deck to be sure it was not a loose or dirty connection there, and still no

If you disconnect the limiter wiring at pin 9 coming from the IF deck, you pickup
a slight "hum", but the popping disappears. I've checked all the wiring going to
the limiter potentiometer (bypassing with jumpers straight from the IF deck to
the front panel). I've also replaced the limiter potentiometer (twice). Here's
where it gets interesting. I took two R-390A's side by side. I wired the diode
load from the bad radio (terminal 14) to the good radio (terminal 15), and no
popping noise. I then reversed the arrangement, wiring the good radio back to
the bad one. Still no popping noise. So with the bad radio feeding into a good
audio deck, no popping, and with a good radio feeding into the bad radio's audio
deck, no popping. Does anyone have any idea where I might look next?
IF deck tips                                      page 75

Date: Tue, 24 Jul 2001 08:47:43 -0700
From: "Roger L Ruszkowski" <rlruszkowski@west.raytheon.com>
Subject: Re: [R-390] Popping noise with the BFO on try 1

I suspect a connector oxide problem. It make look good but them its over 50
years old. I or one of my friends may have dunked the chassis in the TTY
degreasing machine some where back then. It solved my problem of dirt that
day but now its a old age problem. Good eye ball and just good methodology.

There are the like likely areas.
AF deck connectors.          IF deck connectors. The harness on the front panel.

Pull the harness connector back covers off and push the insulation on each lug
up. Look for a bad solder joint. Looking at the schematic will show some pins
need a closer look than other pins.

Drop the front panel and look at limiter and contacts.

Check the BFO circuit.

Most common, One of those connector pins is less than good and giving you a
open between the pin and plug.

Second the stuff you can not see is breaking down and discharges. some voltage
is breaking over and arcs. you hear a pop. The discharge path is come crud you
can not eye ball and can not probe with a ohm meter.

Doing the chassis in the dish washer is not going to get into the connector back
shells where the problem is likely located.

You find it is not in the module side.

Take the chassis modules out. Take the chassis out to the yard with the soap and
water. Open up the likely connector back shells and go to work with the soap
and water.

Give it all a good bath and shake dry. Let it dry in the sun for a Sat and Sunday
after noon.

(Wrong !!!!! Drop it all in a engine block degreaser tank and hang it out to dry for
a week, rotate it and let dry for another week.)
IF deck tips                                      page 76

Date: Tue, 24 Jul 2001 15:27:29 -0400
From: Al Solway <beral@videotron.ca>
Subject: Re: [R-390] Popping noise with the BFO on try 1

About year ago now I was in the process of restoring my Bluestripper from Fair
Radio. I did not turn on power to the radio but dismantled it down to nuts and
bolts except the gear train. Every thing was cleaned and inspected with a 5
power loupe including the harness. Each connector cover was removed as
described by Roger above. I found 2 cracked solder joints. None were actually
open but were potential failures. After cleaning, replacing all the paper caps and
out of spec resistors power was turned on. The radio was alive on all bands. The
radio was aligned, tubes replaced and finally finished on 9 January 2001.
Sensitivity was similar, though not quite as good as what Walter reports on his

Every thing did not go as smooth as it seems. One major problem after replacing
the RF Gain Pot (out of spec) was intermittent and erratic operation oporation of
the gain. Finally found that it was a broken wire inside a wire to one of the pot
lugs. The break was about 1/4 inch back from the lug and just beyond where the
solder wicking ended. Repairing the wire cleared the final electrical problem.

So my point is that what Roger is referring to can cause a multitude of electrical
problems. Intermittents are the worse kind to find and age can make a poor
solder joint so much worse. Inspection can find some of them but not all. I feel
that what Roger suggests is holds a lot of water.
Date: Tue, 24 Jul 2001 15:34:25 -0500
From: "Bill Hawkins" <bill@iaxs.net>
Subject: RE: [R-390] Popping noise with the BFO on try 1

Wonder if the "popping" is an intermittent RF oscillation that becomes audible
when the BFO is on - and not otherwise related to the BFO. But then there is this
neat fault isolation trick of using the diode load terminals of two receivers. What
that hookup does is connect the grounds of the two sets together and add some
capacitance to the diode load line. I'd try it with just the two sets grounds
connected, leaving the diode load jumpered for single set operation. Then I'd try
hanging a small cap from the diode load jumper to ground.
Date: Tue, 24 Jul 2001 14:21:52 -0700
From: "Roger L Ruszkowski" <rlruszkowski@west.raytheon.com>
Subject: RE: [R-390] Popping noise with the BFO on try 1

Real good point that should not get passed over with out some thought.

>Wonder if the "popping" is an intermittent RF oscillation that
>becomes audible when the BFO is on - and not otherwise related
>to the BFO.
IF deck tips                                      page 77

Date: Thu, 26 Jul 2001 21:52:18 -0400
From: "Walter Wilson" <wewilson@knology.net>
Subject: Re: [R-390] Popping noise with the BFO on - SOLVED

Bob Camp wrote: I'd bet you that you have a piece of coax / shielded wire that
is arcing.

You were right. It is one of those tiny little coaxial wires. The bad one goes from
the diode load jack to one side of the Limiter potentiometer. The voltage only
increases to about 15 or so volts at the diode load point when the BFO is turned
on, but it seems to be enough to cause problems. Bypass this wire with jumpers,
leaving all else in play, and it's as quiet as as a mouse after the BFO is turned on.
Lots of folks from this list sent many good suggestions, and I tried many of the
"quick" checks. But I had guessed it might be in the wiring. I had to unsolder
both ends of the offending wire to get it out of the circuit in order to determine it
was bad. This one kept me busy for a while, but at least it's been found. Now
on to fixing it.
Date: Thu, 26 Jul 2001 22:29:14 -0400
From: Bob Camp <bob@cq.nu>
Subject: Re: [R-390] Popping noise with the BFO on - SOLVED

Glad you found it ! It's a pain to fix and make it look right. You can always route
a replacement wire outside the harness but it will look odd. Maybe somebody
out there has a wiring harness they don't need, it'd make the job a little easier.
Date: Fri, 27 Jul 2001 06:28:31 -0400
From: "Walter Wilson" <wewilson@knology.net>
Subject: Re: [R-390] Popping noise with the BFO on - SOLVED

This unit is mostly a Stewart Warner unit. The wiring harness looks very clean,
and I still cannot detect any visible clues even now that I've isolated the problem.
The coax does have the clear cover over the shielded cable. This was one of the
harder ones to find. Until you unsoldered the wire and it's shield, it kept arcing
no matter what else you jumped around. Even when you tried to jump out the
diode load jumper connection right inside the IF deck, this piece of bad coax was
still hanging off the wiring just waiting for enough voltage to arc. I had worked
on this one several times in the past and set it aside, but I decided this time I
would not stop until I found it. I probably have 20 or more hours invested in
this one, simple little problem. This kind of problem is a humbling experience.

Once I get the cable out, I'll let the group know if I can detect any visible signs on
the bad cable.
IF deck tips                                      page 78

Date: Fri, 27 Jul 2001 09:37:38 -0400
From: "AI2Q Alex" <ai2q@adelphia.net>
Subject: RE: [R-390] Popping noise with the BFO on - SOLVED

Good work doggin' that one down Walter. It reminds me of an experience I had
years ago with an open inner conductor on an ultra-fine coaxial line on a VHF
transmitter board. That kind of fault is often tough to find when it only rears its
head under extreme conditions. You are to be congratulated for finding it. Now,
go ahead and enjoy your R-390!
Date: Mon, 6 Aug 2001 14:21:25 -0400
From: "rbethman" <rbethman@home.com>
Subject: Re: [R-390] Fw: Frequency display lamps

If you follow the 1956 Manual instructions, or Chuck Rippel's instructions, you
are tuning the the upper slugs to ONE IF, and the lower slugs to ANOTHER IF.
In fact, you are taking the peak of the crystal filter response and ALSO
broadening it to about 1.6 kc. What most folks miss is that the R-390A/URR and
similar radios were designed to provide for RTTY, voice, CW, AND Multi-
Channel use. To allow for the Multi-Channel use, the receiver was intentionally
set to be a little bit broader than people have really thought. Chuck Rippel's
instructions:       http://www.avslvb.com/R390A/html/if_deck.html

Specifically demonstrate this by the shift in signal generator output frequency
between the upper slugs and the lower slugs. If you sit down and go through
the 1956 manual carefully, you will find that you are doing the same thing
effectively. I am refering to Electric Radio issue #26, June 1991. The IF cans have
a minor modification made. (Horrors! Blasphemy!) Not so! Easily returnable to
original. The methodology in tuning the filters is different also. Throughout
both alignment pieces, the IF is fed 455kc. It is not changed, and the procedure is
different on the filters to tighten them up also.

The ER mods don't putz around with testing umpteen tubes. In my mind part of
the falacy of some "Guru's" is to maintain these radios just as they came out from
the factory. If that is what people want, fine. I have a slightly different agenda.
If I can change the tube lineup with later made miniature tubes that have
significant lower noise figures, tighten the IF bandpass and filter width to what it
"really" can do, then I have a fine vintage quality piece of equipment with better

The results of the author of the mods is that the leakage from the test equipment
finally limited his ability to increase the sensitivity or decrease the noise figure by
any further amount. I agree that cap replacement with orange drops will help.
But that is not the level of improvement that I am after. The sensitivity that I
have gotten to so far is that I CANNOT turn the IF gain down enough to meet
the alignment instructions. The potentiometer doesn't have enough range.
IF deck tips                                      page 79

Date: Sun, 12 Aug 2001 15:12:11 -0400
From: "Warren, W. Thomas" <wtw@rti.org>
Subject: [R-390] Sticky IF slugs

Whoopee, my '56 Motorola IF strip is coming to life. After replacing 18
capacitors and 12 out-of-spec resistors, the strip is mostly working. It's acting
like both the 2kHz and 4kHz mechanical filers are dead (oh, joy!), but the 8kHz
and 16kHz filters do work. The strip has plenty of gain, etc.

Now to the question at hand. Some of the slugs in T501, T4502, T503, and Z503
are mighty hard to turn and/or just plain stuck. What is the preferred way to
loosen up these slugs? Someone said that he used just a little bit of WD-40. I'm a
little concerned about the long term effects of WD-40 on the phenolic coil forms.
How about moderate heat? Anyone tried that? With a heat gun or in a 150
degree oven to loosen up the old stickiness? Sure looking for good suggestions
at this juncture. I've got about 25-30 hours so far just in this IF strip and I'm
beginning to see the light at the end of the tunnel. I certainly don't want to do
anything foolish at this point.
Date: Sun, 12 Aug 2001 16:55:06 -0400
From: Norman Ryan <nryan@intrex.net>
Subject: Re: [R-390] Sticky IF slugs

Hooboy, so close after all that work, I can imagine your concern. Have not yet
encountered sticky slugs (knock on wood, now reaching for my head), so can
only speculate.

I guess it's a question of what's down in there. If it's waxy, maybe a wee shot
from a heat gun, then a milli-squirt of WD-40, if the slug begins to give. What
about a 40 or 60 watt light bulb placed near the IF can for several minutes? Heat
would penetrate more gently than with the heat gun.

Joe's R-390A Zippo not recommended. :-)

I don't feel that the WD-40 would be harmful if you wipe off slug and Q-tip the
phenolic tube right away. YMMV, though, and I may be off base and hope
others who respond will pass on their experiences to the group.

My slug tool is plastic and twists quite a bit with sluggish slugs. The tool
probably would break first before breaking a slug.

Keep us apprised of your progress, OK?
IF deck tips                                      page 80

Date: Mon, 10 Sep 2001 21:56:51 -0400
From: James Miller <JamesMiller20@worldnet.att.net>
Subject: Re: [R-390] on coax short

Well I have confirmed that the crackling noise (with BFO on) was indeed due to
some kind of dielectric breakdown in one of the mini-coax lines running from
the IF module to the diode load terminals, and to the limiter control. Not sure
which of the lines is in question, but I plan to replace all of them. Now the hard
part: Either threading new cables into the wire harness, or run them separately!
The fun begins. Thanks to all who had suggestions!
Date: Tue, 11 Sep 2001 07:38:46 -0400
From: Bob Camp <bob@cq.nu>
Subject: [R-390] forwarded 390a message on coax short

Just for the record I have seen what appears to be military work on R-390's that
did it both ways. If they put in a new wire they then laced over it and the original
wire to hold it in place. In some cases the second lacing job did not stand the test
of time and it came loose. Since you are going to have to re-lace either way I
think I'd pull the old wire and do it right. That way the radio winds up better
than when you started. While you are in there you might just replace anything
that looks like trouble ...
Date: Sat, 13 Oct 2001 16:06:58 -0400
From: Mike Sullivan <michaels@kc2kj.k2nesoft.com>
Subject: [R-390] R390a AGC Help needed

I have a Motorola 390a with a nasty agc problem. Let me provide some

1. Bought at Shelby Hamfest.

2. Noticed AGC problem and "blindly" replaced C547, 551,548 and noticed no

3. While had IF module applied Lankford AGC mod by placing parallel IN4148
diodes accross R547 and R546.

4. Still no luck, got more serious and noticed positive .5 volt on agc line under no
signal condition.

5. Found bad 220 pf capacitor, C 546 that was leaky. Replacing it resulted in
negative agc (~-0.14 volts). Carrier meter now indicates but seems way off. AGC
action still not right.

6. Prepared the following input voltage/Carrier Meter/AGC voltage table to get
a handle on AGC problem:
IF deck tips                                     page 81

Input v.        | Carrier Meter | AGC voltage
- -----------------------------------------------
1        uV                0                         -0.14
10       uV                0                        -0.14
100      uV                2                        -0.14
1000 uV                    52                       - 0.50
10000 uV                   90                       - 4.18
100000uV                   ~110              - 6.68

All measurments taken with a URM-25D, terminated through URM25 antenna

7. One aspect of the problem seems that the AGC delay action is delayed too
much and cuts in too late. However, the distrotion cuts in somewhere between
100uV and 1000uV. A scope set at the grid of 3rd IF amp shows the IF signal
going into positive region of the input and clipping at the stage. It seems like no
AGC is being effectivly applied earlier in the signal chain. However have
measured AGC at IF stages.

Help! I have measured AGC voltage at the RF and 1sr, 2nd and 3rd mixers. The
10 megohm meter loads (or detunes) the rf amp and some of the mixers they do
follow AGC voltage it seems.
Date: Sat, 13 Oct 2001 17:38:24 -0700
From: "Kurt" <radiouser@uswest.net>
Subject: Re: [R-390] R390a AGC Help needed

There are several things to look at to isolate the AGC problem. There are two
basic causes for your problem. 1) a short or leakage on the AGC line pulling the
voltage down or 2) there is not enough AGC voltage being generated. Some
things to try:

0. Remove the mod and fix the AGC problem. Then you can put it back.

1. Make sure the tubes are good.

2. Disconnect the AGC line from the AGC detector and see if the AGC voltage
increases as the input signal increases. A 100 uv input should produce about -4
volts of AGC. If this stage is working ok then look for problems on the AGC

3. Pull out the tubes on the AGC line one at a time starting with the RF amp tube
and working towards the detector. This can help isolate the problem.

4. You can separate the AGC in the RF deck from the IF deck by removing the
jumper on the back of the radio. If you need more help email me.
IF deck tips                                      page 82

Date: Sat, 13 Oct 2001 22:16:04 -0400
From: James Miller <JamesMiller20@worldnet.att.net>
Subject: Re: [R-390] R390a AGC Help needed

On my 390a I found a few leaky bypass caps on the AGC line at various locations
(IF and RF decks). I think these are .005 or .001 (dont have the schematics here).
I basically went through the entire radio and replaced them all. They go bad
with age (yes even the so called unbreakable disc ceramics). And a leaky tube
grid can also pull the AGC down, so check the tubes. And most tube testers
reveal enough grid leak to identify a bad tube as a cause for AGC problems, so
you may have to try them all by hand. 73 Jim N4BE
Date: Mon, 15 Oct 2001 11:28:48 -0400
From: Roy Morgan <roy.morgan@nist.gov>
Subject: Re: [R-390] R390a AGC Help needed

>I have a Motorola 390a with a nasty agc problem....................<snip>

1) Measure all resistors in the AGC circuit. Careful study of the schematic may
reveal ways you can do this withOUT taking the RF section out of the radio. I
suspect you will find at least one high value resistor which has drifted much
higher than it should be.

2) Replace each tube controlled by the AGC one by one with KNOWN GOOD
NEW tube. You may have a leaky tube. Watch the AGC buss voltage with a
HIGH impedance voltmeter.

3) Make resistance readings from the tube pins (the agc controlled grids in
particular) and compare with the manual values.

4) Make sure you have replaced all, repeat all paper tubular capacitors.

There are other more sneaky methods for discovering AGC problems. I include
here some messages from my saved posts file:

>Here's a quick check to see if a leaky C551 is getting you down.
>The best way to test it of course is to apply B+ to the cap and measure its
>leakage current directly but here's one you can do from the comfort of your
>radio listening chair.
>With the radio cold, turn it on, let it stabilize for 10 minutes or so, and
>tune in a calibrator signal.
>Make a note of the Carrier level meter reading in the FAST mode.
>Use the reading in the FAST mode as the reference as C551 is out of the
>circuit in this position. (We will also assume the other two caps in the AGC
>circuit are good.)
>Switch to MED. C551 is now connected from the AGC line to ground. If the
>Carrier meter level drops it is due to C551 leakage.
IF deck tips                                      page 83

>Switch to SLOW and note the Carrier level again. This is even a better test
>since the cold end of C551 will now have some B+ voltage on it from the
>plate of the AGC time constant tube V506A.
>Now let the radio warm up real good for a few hours.
>Repeat the three tests done previously, again using FAST as the reference.
>Comparing FAST to SLOW will show the largest difference (if there is one).
>If there is significant C551 leakage it will be much more apparent now when
>the radio is hot than before. Capacitor leakage will always increase with
>When I did this test with my 390A I could see about 2 dB difference between
>the FAST and SLOW positions when warmed up. Nothing to get upset about
>it does indicate some leakage occurring. Ideally, the carrier level should
>read the same in all three AGC speeds.
>When I originally went through my IF deck, I checked C551 out of circuit
>with 300 VDC applied and measured 0.82 uA of leakage at room temp, which
>increased to 5.6 uA after I warmed it up good with a heat gun.
>At the time I didn't have any good substitute caps to put in and I was
>tackling much bigger problems with the radio, so I just flagged it as
>something to take care of the next time I take the radio out for a few final
>touches that are left to do.
>The toughest part of this test is looking for tiny level differences on the
>small R-390 carrier level meter. Also, sometimes the movements on these old
>meters can be a bit sticky. A VTVM with a large instrument meter or DVM
>connected to the AGC line would indicate AGC voltage differences much
>From: Nolan Lee <nlee@gs.verio.net>
>Cheap insurance. :-)
>Next will come all the other modules, whether they need it or not.
>You've done the hard one, the rest are easy. Make sure when you
>pull the RF deck to replace the three caps in it that you clean
>the hell out of the band switch wafers with some electrical
>cleaner that doesn't leave any residue. Any accumulation of
>dirt. oil film, etc. on them can lead to flash over of the B+
>ruining the wafer. It's a pain to change one, too. ;-(
>The most common arcing path that they seem to take is to the
>switch shaft so make sure that you clean the movable center
>sections of the switch too.
>Don't forget to check the little oil filled nut mount chassis
>capacitor near the 6DC6 for electrical leakage. If you're lucky,
>it will be fine. It's a pain to change one.

Good luck, and please report the cure when you do find it. Roy
IF deck tips                                      page 84

Date: Sat, 20 Oct 2001 16:40:07 -0700 (PDT)
From: MICHAEL OBRIEN <mikobrien@excite.com>
Subject: [R-390] Thanks for help with hq-180 avc problem

I would like to thank everyone for their help and tips on fixing my HQ-180 AVC
problems. I would also thank Les Locklear for the table of voltages to check. I t
showed i also had a gain problem. The problem was traced to a bad tube socket
pin for one of the 455 if tubes. The hq-180 has joined the rest of my SWL station
(sw-8,frg-7, frg-8800,hq-145a and brand new yaesu vr-5000) where it is doing a
very nice job of keeping up with the newer receivers. Now to find the time to
work on my SP600 and R-390a.
Date: Tue, 6 Nov 2001 12:46:54 -0500
From: twleiper@juno.com
Subject: Re: [R-390] Frequency Stability Mystery Solved

> Further frequency monitoring reveals that with the thermostat
> set at 105F, the temperature up-down cycle is so long and
> slow (5-10 minutes) that the frequency changes by up to 50Hz.

That's becuase there is no adjustable "heat anticipator" function in the thermostat.
They probably pick the best temperature that "resonates" with the thermostat
and "cold" ambient temperature. But there IS a reason they only say to use the
ovens in cold operating conditions, and this certainly is it. In other words,
turning the ovens on does not give you better stability under normal conditions,
but will improve things under cold conditions, especially during warm-up. For
the most part, crystals are stable at any temperature, so it is just a matter of
keeping the oven constant at "some" temperature. You could, in other words,
use a refrigerator instead of an oven. To the degree that the oven temperature
differs from that of the ambient temperature, regulation can be more precise
because the "flow" of heat out of the oven (or into the refrigerator) is larger and
easier to control.

For instance, at "normal" oven temperatures you could do away with the
thermostat all together, or simply use it for over-temperature protection. I
would experiment with simply inserting a series resistance or dropping the
voltage to the heater to the point where it is held "on" by the thermostat at all
times, and see where the temp ends up. Another clever modification would be to
put an ajustable resistance ACROSS the thermostat contacts. In this case, you
would adjust the "off" current up until the thermostat is just barely "off" at all
times. The benefit to this configuration is that it would still allow rapid warm-up,
though it might over-shoot for a little while. Either way you do it, the above
type of operation will provide very stable oven temperature that is minimally
effected by changes in ambient temperature... and NOT effected by complex
heater, insulation and thermostat hysteresis characteristics.

Just what we need here, a transition to an HVAC design round table...
IF deck tips                                      page 85

Date: Tue, 6 Nov 2001 12:10:53 -0800
From: David Wise <David_Wise@phoenix.com>
Subject: RE: [R-390] Frequency Stability Mystery Solved

> the ovens on does not give you better stability under normal                        [snip]

I wouldn't be surprised if it were better with the t-stat at the stock temperature,
but I don't want to give my VFO that kind of beating. There's a reason it's not
recommended except extreme cold/hot. (Yes, they recommend running the
ovens in desert conditions "because of the large difference between daytime and
nighttime temperatures.")

> For the most part, crystals are stable at any temperature, so it is
> just a matter of keeping the oven constant at "some" temperature.
> You could, in other words, use a refrigerator instead of an oven.

They went so far as to pick crystals whose TC goes through zero at
approximately the oven temperature, so the cycling would cause minimum shift.
They did something similar with the VFO. The Final Engineering Report has a
VFO frequency-vs-temp graph (Figure 68)
which shows that their intent was for it to be on-freq at 25C and 70C.

> To the degree that the oven temperature differs from that of......

I believe that. When the Final Engineering Report started talking about damping
in the context of temperature vs time, I knew I was in over my head :-|

> a..........put an ajustable resistance ACROSS the thermostat..................

If I hadn't buttoned up the VFO (and what a nitpicky process that turned out to
be!), I'd do that. As it is, if it bugs me enough I'll put in a time-delay relay to run
the ovens 15 minutes and then off. All I want is a quick warmup. Overshoot is a
known issue. According to the F.E.R., the Signal Corps wanted a 15-minute
warmup. Collins tried and tried but the best they could do was a 30-minute
warmup, with, get this, the biggest error at exactly 15 minutes.
Date: Fri, 23 Nov 2001 16:07:07 -0500
From: Mike Sullivan <michaels@kc2kj.k2nesoft.com>
Subject: [R-390] r390a agc problem finally fixed

This is a followup on the r390a I bought at Shelby hamfest that had an AGC
problem. I finally fixed the beast. After replacing every capicitor in the AGC
chain including capacitors in the RF deck, fixing two burned out resistors and still
not getting proper AGC action I got serious and found low resistance in the AGC
line. Seperated RF deck from IF deck and traced low resistance to IF deck. Traced
problem to a poor solder joint (with solder splash) shorting signal return of
mechanical filter to ground. Interestingly, the filters all appeared to work, but the
short prevented AGC voltage from being applied to second IF amplifier.
IF deck tips                                      page 86

I suspect that problem appeared in receiver after replacing the mechanical filter
and that receiver was placed "on the shelf" for further repair later. Problem was
tough to find (for me), given the poor quality of soldering, might have been
beyond repair capabilities of tech, but who knows.

At least this fine old receiver is now hearing signals properly!

Date: Mon, 26 Nov 2001 14:09:52 -0800
From: "Roger L Ruszkowski" <rlruszkowski@west.raytheon.com>
Subject: [R-390] 390A AGC Circuit Problems.

I have a similar problem (maybe exact same problem) with my AGC. Expecting
more caps need replacing I have been avoiding the problem. Great Ideas on
where to start on this circuit. Years on the bench and I am still amazed at what I
do not know about these receivers.
Date: Wed, 5 Dec 2001 09:57:23 -0800
From: David Wise <David_Wise@phoenix.com>
Subject: RE: [R-390] Nice package for sale

> The radio was restored by me and has been running fine
> for the last year, except the BFO coil recently got a little
> squirrely. I have a replacement and can fix if needed, or..............

I just fixed a BFO problem. After a couple hours of warmup, mine would
suddenly jump a couple hundred hertz. Then it would stay there. Turned out to
be slight oxidation on the mounting screws for the stud-mount cap and choke
inside the can. This is an easy R & R, with only one caveat: DO pull the shaft out
of the chassis before trying to remove the bellows coupler.
Date: Wed, 5 Dec 2001 11:32:02 -0800
From: David Wise <David_Wise@phoenix.com>
Subject: RE: [R-390] Re: Baluns

> using before. Several strong stations now pin the carrier
> meter, and the receiver is obviously overloaded. Spurious signals are now

No kidding! With a very strong signal, there's enough AGC to cut off the AGC
time-constant tube V506A. At that point, there's enough current to put the
meter just at full scale (or maybe a little above). The only time you'll get higher is
when the 4th IF V504 is drawing grid current. (This is what makes the meter
deflect in MGC mode.)
IF deck tips                                      page 87

Date: Mon, 10 Dec 2001 09:16:36 +0200
From: "Bryce Ringwood" <BRingwoo@csir.co.za>
Subject: RE: Meter Cal (was RE: [R-390] Re: Baluns) - Dumb Question

Is there a relationship to 'S' units ? I have an idea in the back of my mind (what's
left of it) that 100uV = S9 or something like that.
Date: Mon, 10 Dec 2001 07:48:23 -0500
From: Bob Camp <bob@cq.nu>
Subject: Re: Meter Cal (was RE: [R-390] Re: Baluns) - Dumb Question

One part of the calibration procedure on the R-390 is to set the IF gain pot. When
you do this you set up a relationship between the S meter and the input to the
radio on a specific band. It also sets up a relationship to the voltage on the diode
load test point. Unfortunately there is no standard point for S9 in general. Some
radios have 100uv as S9 others have 100uv as 20 db over S9. That makes signal
reports a bit of a mess .... These days the standard way to set up the IF is for best
sensitivity (noise figure). That will give you a different S meter reading than the
old approach. In general we set the IF's up to be have less gain than the old way.
The net result would be that if 100uv = S9 per the old way then maybe 250uv =
S9 when you do it the new way.
Date: Tue, 11 Dec 2001 13:19:54 -0800
From: "Roger L Ruszkowski" <rlruszkowski@west.raytheon.com>
Subject: Re: [R-390] Ye Olde How to.

>One thing I have pondered is how to operate the IF strip outside the receiver
>(where I can poke around with a 'scope while it is operational.
- ------------------
You can pull the IF deck free of the chassis and get it out. Turn the receiver up on
end with the IF deck End down on the bench. Lay the IF deck on its side
alongside the receiver. You then plug the IF deck cables back in and operate the
receiver. You can probe into the IF deck as needed. This also works for the
Audio deck if you need to go into there. You can turn the receiver up on the
other end and do the RF deck. However we have some aversion to pulling the
RF deck.
Date: Sat, 15 Dec 2001 08:28:15 +0100
From: "Claudio Spiritelli" <oldradio@tin.it>
Subject: [R-390] ACG problem

 This is my first post on this list. I just finish to rework my 390A and I was very
happy with the result. Perfect reception on AM on all bands, and very good
sensitivity. SSB was not perfect therefore I decided to make the Lankford
modification. Results on SSB were great, but whenI went back to AM , I had a
surprise. With maximum RF gain, on a strong signal, the ACG is not working
properly ( I am assuming) and I am having a lot of distortion that goes away as
soon as I diminish the RF gain.
IF deck tips                                      page 88

 I could reverse the modification to see if the cause was that one or if something
else did happen while I was working on the unit. I decided to ask to this audience
in order to have more inputs on the possible cause and how it can be resolved
without taking the modification out ( it works great on SSB).

 The modification is usual , with the 2 diodes and 47 pF in parallel to C535. I did
not use 1N4148, but some other unknow diodes.
Date: Sat, 15 Dec 2001 07:39:51 -0500
From: "Dan Martin" <dmartin@visuallink.com>
Subject: Re: [R-390] ACG problem

Regarding a quick evaluation of the 390A AGC circuitry, you can check the
resistance to ground of two pins, one on the r.f. deck and one on the i.f. deck.
Male pin 6 on J512 on the i.f. deck is the AGC line throughout the i.f. deck. It
should read "open", or infinite to ground. Any less than this and you may have
leaky AGC bypass caps. Similarly, check pin E (J208E) on the r.f. deck. This is the
AGC line running throughout the r.f deck. All of the manuals I've seen (Y2K and
Dec. '61 TM) will spec this r.f. deck AGC pin at infinite, just like the i.f. pin.
However, on the r.f. deck AGC line there is a high value 1.5 megohm resistor
(R234) paralleled to ground with C226, one of many .005 uF bypasses, near the
6DC6 at the end of the AGC line. As a result, I think 1.7-1.8 megohms, or so, is a
typical figure for J208E and the 'infinite' may be a typo. At least a couple of us on
the 390 reflector have noted this. Others, make comment, please, if you have a
point of view.

Finally, when making very high value resistance readings such as AGC line
checks, be aware that some modern DMM's (like my Fluke) may "give up" and
indicate infinite whereas a decent analog meter, such as an HP-410C, may go on
to settle at a very high but still measurable value of many megohms.
Date: Sat, 15 Dec 2001 11:55:43 -0800 (PST)
From: Joe Foley <redmenaced@yahoo.com>
Subject: Re: [R-390] ACG problem

So far, Claudio, you're right on the money! The distortion is on the SSB as well
when listening to a strong station. I sometimes have to reduce the RF gain to
about 7 to tune them in. I don't know of a fix to the problem, I just live with it.
Its really only a problem when listening to a weak station talking with someone
on a much stronger station, then I have to "ride" the RF GAIN.
Date: Sat, 15 Dec 2001 20:43:20 -0500
From: "John KA1XC" <tetrode@worldnet.att.net>
Subject: Re: [R-390] ACG problem

If the distortion you hear is severe, I'm thinking that those unknown diodes you
put in might be the source of your problem. That IF AGC amp can generate a lot
of voltage swing, perhaps the diodes are breaking down under large signals.
IF deck tips                                      page 89

This will cause loss of AGC control which will further increase the IF AGC
voltage and so on. Take a look at the AGC and diode load voltages at the rear
terminal blocks when the problem occurs. If the AGC becomes less negative
and/or diode load becomes more negative it means your losing AGC control,
detector overload quickly follows.
Date: Sat, 15 Dec 2001 22:21:03 -0500
From: James Miller <JamesMiller20@worldnet.att.net>
Subject: Re: [R-390] ACG problem

Try removing the diodes temporarily to see if the problem goes away. There
may also be a bad capacitor somewhere on the AGC line. Additionally, if
someone lubricated the gear on the antenna trim shaft, the oil could be creating a
path to ground. The antenna trim shaft is actually insulated because the trimmer
capacitor, inside the aluminum can, is actually tied to the AGC line at the RF
amplifier. Oil contamination can cause poor AGC response.
Date: Sun, 16 Dec 2001 00:17:44 -0800
From: "Bill Smith" <billsmith@ispwest.com>
Subject: Re: [R-390] Odd AVC effect or?

> I agree it does not sound like a tube problem.(therefore all tubes are now very
suspect) <snips>

Yep. That's what it seems to be, all right. I have three 6082 regulators, all of
which are not very good. One tests with what seems to be extremely high GM,
another has what might be good GM, but the needle on the tube tester falls off
quickly, and the tube fails the life test on a Hickok 752A. The third tube is just a
roasted toaster, no emission left. I had monitored the B+ through the test plug
on the side of the reciever. Voltage was stable, but low, then suddenly move in a
ramp up to 190 volts, then would drop to 130 volts, or so, then slowly build
again to 190. Think there is a grid problem in the 6082 with high emission. I
replaced the tube with the high GM and now the voltage is stable at 175 volts. It
takes a while to get there, so likely both tubes now in the set should be replaced.

> Sure it quits oscillating after it heats up,
> But is the receiver operating at its best?
> I just suspect the receiver would be better off
> if you tracked the part down and replaced it.

Still working on suspect capacitors. 2 down, and counting. I was looking at E208
again, and all seems fine, except on band 3, where the bias goes quite a bit more
negative than on other bands. Is this normal? I noticed that special switching
occurs on that band. Haven't fully explored the circuit yet, or measured V203's
(6C4) cathode voltage or current via P221.
IF deck tips                                      page 90

Date: Mon, 17 Dec 2001 14:56:02 -0800
From: David Wise <David_Wise@phoenix.com>
Subject: RE: [R-390] Odd AVC effect or?

Either that 6082 has grid emission, or the tube controlling is has trouble. You're
right on top of it now. Does it pass your tube tester's Gas test? Let the tube
warm up for 5 minutes or so before trying it. Here's one scenario: At 130V, the
6082 has way more V across it than usual so power dissipation is up. The grid
gets hot enough to emit, which drives it positive. When it's up there, V across
the tube is down, it cools off, and the grid stops emitting. Now the cathode is
tired and V falls back below normal. Rinse, lather, repeat. As Roger said, a
[thermal] relaxation oscillator.
Date: Wed, 19 Dec 2001 09:38:29 -0500
From: "Steve Hobensack" <stevehobensack@hotmail.com>
Subject: [R-390] bfo ripple

I wonder if anyone has had this problem and know of a fix. When I first turn on
my r-390a (1963 imperial) and its cold, there is a slight ripple on all cw and ssb
signals. It is very weak. I have checked the decoupling cap in the bfo circuit,
checked the ac filament line which includes the rectifiers, 3tf7, vfo 6ba6, bfo 6ba6,
checked and replaced tubes in that line (thought it was a k to f short). After about
a 3 hour warm-up, the problem goes away. Any ideas? Thanks........Steve KJ8L
Date: Wed, 19 Dec 2001 11:28:15 -0500
From: "AI2Q Alex" <ai2q@adelphia.net>
Subject: RE: [R-390] bfo ripple

Have you checked the electrolytic filter caps? It sounds like you have excessive
power supply hum. Is the ripple 60 cycles or 120 cycles? if you can discern which,
that will tell you whether it's a power supply problem, or leakage, etc. The 120
Hz hum indicates a p/s problem, due to the full-wave rectification, but possible
poor filtering. By the way, recently I had a bad 60-Hz hum problem on a 51J-4
that I was restoring. After 30 minutes it would start up, and get progressively
worse over time. I used an old Heathkit signal tracer to locate it. When I got to
the last IF stage, the tracer's probe was quiet when placed to ground, but
hummed when placed on a grounded terminal strip lug nearby. Huh?
Tightening the lug's mounting screw with a SpinTite wrench eliminated the hum-
--it was loose!
Date: Thu, 20 Dec 2001 08:43:32 +0100
From: "Claudio Spiritelli" <oldradio@tin.it>
Subject: FW: [R-390] ACG problem

Thanks for the help on the ACG problem. I did resolve completly the problem
by using a good pair of new 1N4148 diodes and a 30 pf capacitor. After I adjusted
the neutralitation, the receiver is doing a great job on SSB as well on AM even
with big signals ( ACG voltage up to -6-7 volts). I have an R-9000 Icom receiver,
IF deck tips                                      page 91

but beleive me, I do enjoy more to R-390A , it's a different feeling , tone, and
everythink. I may have to ask some more help in the future. I had to recalibrate
a couple RF transformer ( Z202- Z204) twice at a distance of few days, I am
not sure yet if it is becouse I did reassemble the unit and they were out of
position or if there is other reasons. I still need to investigate and also to see if it
will happen again.
Date: Fri, 21 Dec 2001 08:31:06 -0500
From: "Steve Hobensack" <stevehobensack@hotmail.com>
Subject: [R-390] Z-503 can

Did you see the z-503 can that went on Epay for $44.62? Item nr 1308649212.
Date: Fri, 21 Dec 2001 08:59:14 EST
From: Llgpt@aol.com
Subject: Re: [R-390] Z-503 can

P.T. Barnum said it best............. It is a higher than normal failure item, but they
can be repaired, it's almost always a broken wire caused by the plastic piece
turning inside.
Date: Fri, 21 Dec 2001 09:35:29 EST
From: Llgpt@aol.com
Subject: Re: [R-390] Z-503 can

If the problem is fixed, the price is irrelevant IMHO.
Date: Fri, 21 Dec 2001 09:33:43 -0500
From: "rbethman" <rbethman@home.com>
Subject: Re: [R-390] Z-503 can

Being the one whom won the bid, I can tell you it isn't a broken wire. The slugs
are cracked, and other such things in this Collins s/n 35 IF deck that I'm trying to
resurrect. Sometimes the supposedly ridiculous price has good reason.
Date: Fri, 21 Dec 2001 09:48:00 -0500
From: James Miller <JamesMiller20@worldnet.att.net>
Subject: Re: [R-390] Z-503 can

As one having two 390a's on the bench, one working perfectly, one a basket
case, and another on the way (with its Collins case), I enjoy being one of
Barnum's subjects. Yes an average of $700 a pop. It ain't the money, it's the fun!
How many of us own boats? Not me, that's like pouring money down a rat
hole. How many of us blink an eye as we drive our new Lincoln's off the lot at a
immediate 15% depreciation? How many of us pay income taxes? And what
about those golf $1000 golf clubs? Don't forget booze and cigarettes. Yep
indeed, there are a lot of us born every minute! Now I'm driving over to the Fla
west coast to pick up my latest. Happy holidays everyone!
IF deck tips                                      page 92

Date: Fri, 21 Dec 2001 10:02:33 -0500
From: "rbethman" <rbethman@home.com>
Subject: Re: [R-390] Z-503 can - The rest of the story

The Z503 can at the "ridiculous" price is also an NOS can. It is a spare that never
got used. I managed to get a Z501 can innards for postage. I guess you could say
it all evens out I've bit off a healthy hunk of restoration. I've got my hands on a
Collins R-390A s/n 232. It sure has seen a lot of service, but with the exception
of one 26Z5W, it is ALL there - even the ballast tube! I've never seen one before
this. The only non Collins component is the PTO which got changed somewhere
during maintenance with a Cosmos. I have an individual that is willing to trade
across the board a Collins PTO for the Cosmos PTO.

The front panel shows the use it got. There is an arc of wear around the Kc knob
that has worn through the gray, the primer, and is down to bare aluminum. The
arc around the Mc knob is only into the primer. There looks to be two cans in
the RF deck that have been replaced over time. It has only one fuse, and is
marked with "Mod 1" on all modules except the PTO. It has sat in DRY storage
for sometime, with no or VERY little corrosion.

Yep! Another E-Pay item. Paid less than a Fair Radio unchecked one. (Shipping
is another matter) The meters are the original Simpson's. I can tell you that the
lower part of the bezel being bent in is NOT an operator's idle hands. The VU
meter lower part of the bezel is bent in, but it is too straight and true to be
anything but machine stamped.
Date: Fri, 21 Dec 2001 19:36:49 -0500
From: "John KA1XC" <tetrode@worldnet.att.net>
Subject: Re: [R-390] Z-503 can

Mike, give Fair a call/email, they can often get parts from junked modules. I
bought a used Z-503 for $12 a couple years ago from them and it got the radio
going again.
From: "Steve Goode" <goode@tribeam.com>
Date: Wed, 2 Jan 2002 10:42:22 -0600
Subject: [R-390] AGC operation question

This Christmas vacation was a good one for my R-390A and me. I finally got the
rig back together after recapping, cleaning and fixing a PTO problem. It is
working very well now. I have a question about the normal operation of the
AGC switch. In this radio, if I start at the slow AGC position and switch to the
medium position, the radio is muted for about two seconds and then slowly
comes back to the proper level. Switching between the slow and fast positions
does not exhibit this muting. Is the muting normal in switching between slow
and medium?
IF deck tips                                      page 93

From: "Scott, Barry (Clyde B)" <cbscott@ingr.com>
Subject: RE: [R-390] AGC operation question
Date: Wed, 2 Jan 2002 10:52:30 -0600

If I'm not mistaken, this is proper operation and I think it's mentioned in the
manual. Mine does the same thing.
From: "Michael P. Olbrisch" <kd9kc@elp.rr.com>
Subject: RE: [R-390] AGC operation question
Date: Wed, 2 Jan 2002 16:59:22 -0000

Mine does this too. Never gave it any thought, but since it don't arc or smoke
when it does it, I guess it is OK.
From: Llgpt@aol.com
Date: Wed, 2 Jan 2002 12:25:21 EST
Subject: Re: [R-390] AGC operation question

Perfectly normal, often referred to as the moment of silence. Les
Subject: Re: [R-390] 6080 in place of 6802 - RMS ???
From: "Roger L Ruszkowski" <rlruszkowski@west.raytheon.com>
Date: Wed, 9 Jan 2002 11:38:32 -0800

<snip>..........I am using 12BY7 myself for the 3TF7. I did have a jumper in the
socket and used 2 12BA6's for the BFO and PTO. But a diode poked into that
socket would much simpler to install. I do like the 6BA6 5749 tubes better than 2
12BA6's. When I when through my last noise reduction drill over Christmas, I
found I had no way to judge the noise of the 12BA6's in the PTO and BFO
circuits. By using the 6BA6's, I was able to select 2 very quiet 6BA6 tubes and use
one in the PTO and one in the BFO. Selecting 6BA6's in the first IF tube socket for
best noise is more sensitive than using the BFO or PTO socket.
From: "Chuck Rippel" <R390A@R390A.com>
Date: Thu, 10 Jan 2002 12:26:09 -0400
Subject: Re: [R-390] SP600JX17 - drift

All very true and good points Barry. A good bit of the drift problem may be
caused by the chassis expanding with heat. The SP-600 chassis is not the most
robust on on the block and not near as immune to flexing as say, the R390/or
the "A" variant.

The regulator I install keeps the filament voltage dead on and even compensates
for resistance changes in the actual tube filaments to maintain the same current
flow value. The radios still drift. I would suspect they would drift if you
regulated every voltage applied as the problem does not appear to be electrical
in cause.
IF deck tips                                     page 94

The radio still drifts. Les Locklear pointed out in a conversation we had last night
that you can pass your hand over the VFO tube on top and if the BFO is on and a
station tuned it, the receiver will "pull" just a tad.

I accept the drifting as a part of the personality of the SP-600 family of receivers.
BTW having the special tube shield on the VFO oscillator tube that anchors to the
main chassis has little effect on drift. That the original is there or its been
replaced with an IERC makes little difference.
Date: Thu, 17 Jan 2002 08:28:08 -0800 (PST)
From: <jlap1939@yahoo.com>
Subject: [R-390] SSB and the 390

Since no one has fought this it seems for some time:

At the risk of ridicule, I am going to give an effective method of BFO setting to
"0" by using your ears, And also remind that the correct method always works,
provided that alignment is very good on the unit in question. I do this in
response to a few inquires I have had and because many still believe people like
me, who listen to obscure SSB transmissions are confused at best..If you haven't
gotten into it, you should try it..With this method you can find very weak
/obscure stations...

May I remind you that after you (in my case), obtain a properly aligned unit,
(including many others in addition to the 390 series,) or else have aligned your
own unit, including neutralization..that you may want to check VERY CLOSELY
for "0" on the BFO. This is to allow accurate frequency setting and readout, that
can well surpass your ability to visually resolve the VR counter.

First the correct method..::( Isn't it?)

 Find total quiet place, then also disc. ant.
 Set bandwidth at 0.1.
 Leave BFO OFF, Turn to Cal. on function.
 At any 100 kc point, tune to FIND the point that produces an increase on the
carrier meter. (it may be very tiny, so watch carefully. You may want to "rock"
back and forth).
 Now set bandwdth at 2 or 4 or even more on some.
 Turn on BFO
 Zero-beat the sig. (re-check)
 Set knob at "0".(either internally or by the knob)

Hope I did this right...

However, a Sig Corps Sgt. named Stone, (yes he was related to Sgt. Rock),
showed me this:

"Good aligned radio...take off the BFO knob..go to dead spot, disc. ant, use cans,
turn on BFO..LISTEN! Turn BFO shaft..(if you can't, you're a -----,) and tune to
IF deck tips                                      page 95

lowest sound generated by the BFO, by "rocking". Do several times. You will be
more accurate than with any other procedure. replace knob at "0"". (this is the
way I wrote it down 40 yrs ago.)

I do this, and know that it is best for me. I can tune to a freq. where I know that
activity will be encountered, that is exact, w/PLO unit, and then tune my 390 (of
course + or - for each sideband, after CAL. at the nearest 100), and I am more
accurate, based on the voice freq. produced, than with the cal. set system. It
works on my SP-600 well also, but is not as accurate. In other words, I can go to
a given freq., and when the traffic starts, I will be tuned "perfect". I start about +
or - one and one half on the 390 non a.

To really bore you, I give the reasoning:

Visual resolution nowhere near equals audible. (See many sights on web.) If you
watch the meter, you will never get optimum, as your vision is not that sharp.
By using the natural sound of the BFO while not encountering a signal, you can
find its LOWEST sig. point. (Many persons can detect a change of as little as 3
cents, and most at 4 or 5 cents. There are 100 cents in a semitone, (which is for
example, C to C# on the music scale.) I suggest that this is a figure that will be off
in freq. by a very small figure. Of course it would depend upon how accurate
YOU could actually be, and a "tonally challenged" person might not do very
well...so don't hold me too much at blame if it doesn't work.. It might be worth a
reminder that good SSB, WITH OR WITHOUT a converter, is something you
need to LISTEN for, and take the time to learn. You will have to find a result that
gives the correct sound for the voice, so it is the same as if that person was
standing right beside you. In addition, because you are encountering many diff.
levels of strength with set internal generator, you must keep the RF gain
reduced... Those who don't agree, please forgive the foregoing.
Date: Thu, 24 Jan 2002 08:49:09 -0800 (PST)
From: John Kolb <jlkolb@cts.com>
Subject: Re: [R-390] What is the Crystal in the 51J filter ?

> I am restoring a 51J the crystal filter section is missing, so I am
>rebuilding it, I can make up a switch, and even a differential capacitor. So, what
is special >(if anything) about the 500KHz crystal.

I don't know what crystal was used in the 51J xtal filter, but the usual 455 kHz
xtal filter xtal was a small black plastic case with solder lug terminals coming off
both sides, for lower shunt capacity across the filter than the FT-243 or other
holders of that period. I would expect an HC-6 holder xtal would work well, the
version with long wire leads even better. Bend the leads at right angles as soon
as they leave the case for lower stray C. Wire up the xtal filter with heavy stiff
wire, running straight from point A to point B, rather than looped in a circular
path for stability. At the same time, the circuit should be arranged to have as
little stray C as possible.
IF deck tips                                      page 96

From: "Jim Temple" <jetemp01@athena.louisville.edu>
Date: Fri, 25 Jan 2002 13:35:29 -0500
Subject: [R-390] Stuck slugs

In aligning the fixed IF in my "massacre" rig, I have found that the bottom slugs
in the T501 and 502 coils are stuck. Any advice as to how to unstick them without
breaking them? I have considered a hex wrench that fits the slug to overcome
the whimpy plastic wands I have.
Subject: Re: [R-390] Stuck slugs
From: "Roger L Ruszkowski" <rlruszkowski@west.raytheon.com>
Date: Fri, 25 Jan 2002 12:58:42 -0800

<snip> Pull the can tops off the transformers.
Dial the top slug all the way out of the transformer so you can work on the
bottom one.

A hex key is an acceptable way to work a tight slug loose. Think about it and do
not over force it. The transformer slug can be adjusted from the bottom through
the chassis deck.

Pull your deck up and look into the bottom to see if you get any clues.

Likely the wax has gotten hot in storage and bound the slugs. A bit more force
than expected will pop them loose.

Pull the covers and the deck and look first.
No reason to get surprised

The fellows will give you a list of solvents to try.
My list or solvents from the 1970's is not OSHA or group approved.
We don't do that any more.
Date: Fri, 25 Jan 2002 16:25:00 -0500
From: Jim Brannigan <jbrannig@optonline.net>
Subject: Re: [R-390] Stuck slugs

If you can get at the slugs with a hair dryer, heat them, it might help. The last
time I took a hex wrench to a slug it took me two days to completely
disassemble the unit.

A week to wait for the new slug to arrive mail order ( I got lucky finding one)
and another two days to re-solder the leads to the coil (they broke off when the
form twisted from the hex wrench torque) and reassemble the unit. Then I could
finish the alignment. Just a thot
IF deck tips                                      page 97

Subject: Re: [R-390] Stuck slugs
From: "Roger L Ruszkowski" <rlruszkowski@west.raytheon.com>
Date: Fri, 25 Jan 2002 16:57:05 -0800

If you can get at the slugs with a hair dryer, heat them, it might help.
From: "Claudio Spiritelli" <oldradio@tin.it>
Date: Sun, 27 Jan 2002 10:50:02 +0100
Subject: [R-390] Popping noise problem

Hello to all, I just discover a problem with my 390A. In order to ear the problem
I must do the following:

RF gain .......... completely CCW
Local AF gain......completely CW
Limiter ...........OFF

In this situation there is a "creaking" and "popping" random noise in the speaker.
During normal operation is very hard to ear and only in presence of weak signal.
I tried to localize the source of the noise by "sectioning" the receiver. The AF
section does not produce the noise, as well as the RF section. The source appears
to be on IF section. I did section more deeply and I removed the "Diode Load"
jumper and the noise is still there. This make me to believe that the source is
between the "Diode Load jumper" and the first AF amplifier, witch leaves only
the "Limiter". Analyzing the noise with a "scope", I see the noise as a very short
but high spike on the "signal line" in the "limiter" section ( actually when the
Diode load jumper is in place, the noise propagate backward to the detector as
well). On the B+ line , I see low frequency variation ( with the scope at is
maximum sensibility of 1mV/div) witch I think is the "filtering" trying to bypass
the spikes, so I am assuming that the noise is not coming from there. When I
turn the limiter on, the noise disappear on the audio as well as I do not see it with
the scope and the B+ line does not have any low frequency variation. That made
me to believe that the capacitor C536 was the cause. Wrong.

There are not to many other components in that section that can cause such a
noise and after I replaced the tube ( 5814A), I did run out of options. One more
piece of information, it appears that the noise goes away after the receiver is on
for more the 1 hour.

Unless my analysis is wrong and the noise has different source, I need some help
from the experts.
IF deck tips                                      page 98

From: "AI2Q Alex" <ai2q@adelphia.net>
Subject: RE: [R-390] Popping noise problem
Date: Sun, 27 Jan 2002 09:49:36 -0500

Thanks for your posting. Recently, I had a 1958-vintage Collins KWM-1
transceiver on my bench. A block-style mica capacitor in the set's product
detector was operational, but noisy as all get-out.

In the KWM-1 circuit, in Standby mode, audio from the set's product detector
was fed into the set's AF amplifier string, along with sidetone when on CW, and
I could hear that puppy crackling away like mad in the loudspeaker when I was
transmitting, and of course it was "in the background" on receive, although well
masked by incoming signals.

I zeroed in on it by sectionalizing, as you're doing, using a signal tracer and

It was a satisfying feeling to clip it out and see all the noise go away.Finding it
was relatively easy; replacing it was tricky (very tight quarters), but now all's
well in KWM-1 land.

Good luck. You'll find the bad part--and then you'll be very happy!
Date: Sun, 27 Jan 2002 09:46:31 -0500
From: James Miller <JamesMiller20@worldnet.att.net>
Subject: Re: [R-390] Popping noise problem

I had the same problem with my 390a. Someone on the list suggested that the
miniature coax cables were experiencing a breakdown of the center insulation
due to aging. After some experimentation, I discovered that was indeed the
problem. After replacing the coax cables from the IF module to the diode load
connector, and from there to the Limiter control, my problem was fixed.
Apparently the little coax cables begin to break down with age. Unfortunately
this can be a tedious job! Jim
From: "Walter Wilson" <wewilson@knology.net>
Subject: Re: [R-390] Popping noise problem
Date: Sun, 27 Jan 2002 13:43:08 -0500

That was indeed my problem on one R-390A. I replaced the coax between the
Diode Load and the Limiter pot/switch, and the problem disappeared. To
confirm this before you break into the wiring harness, you'll have to disconnect
the existing coax at BOTH ends, and patch in a substitute piece of coax.
IF deck tips                                      page 99

From: "Claudio Spiritelli" <oldradio@tin.it>
Subject: RE: [R-390] Popping noise problem
Date: Sun, 27 Jan 2002 23:52:00 +0100

Yes I did change the capacitor as well as I did change all the capacitors around the
limiter (C549,C532,C536,C531) the only one I did not change yet is C537. I am
convinced that the noise is generated on this section , as a matter of fact even
without C531 and C549 ( section completely isolated) the noise persist since I can
see it on the plate (pin1) of V507 with the scope, this test should also eliminate
the suggestion from James ( coax cables to the Diode Load). I am afraid that the
problem is on the socket of V507. Is this possible? Or should a pay attention to
the resistors as well? or am I overlooking something?
Date: Sun, 27 Jan 2002 23:29:20 -0500
From: James Miller <JamesMiller20@worldnet.att.net>
Subject: Re: [R-390] Popping noise problem

My posts don't seem to be making it through, so I will try again:

> A follow up...
> On my 390a if I recall correctly the popping would NOT occur as much
> when the RF gain was cranked down. It seemed to occur more when the RF
> gain was at maximum and there was a strong signal, which meant the diode
> load voltage was at it's highest magnitude...hence the coax insulation
> would tend to break down (causing a pop) when the RF gain was full up
> and a strong signal (AM or carrier) was present. Claudio mentioned that
> he hears it when the RF gain is turned down (full CCW)...so maybe
> (hopefully) his problem is not coax related. Just a thought.
> Someone emailed me asking for me to discuss the procedure I used... So
> here it is...If it has been determined to be the coax that is bad, you
> can either attempt to thread new ones through the wiring harness or
> leave the bad coax as is in the harness and route the replacements
> separately, perhaps using tie wraps to secure them to the outside of the
> harness. I chose to remove the old coax and thread replacements through
> the harness. Believe it or not, I succeeded in doing this while leaving
> the lacing reasonably intact. The replacement coax should be the very
> small stiff variety with smooth plastic cover (RG-174 I believe). The
> stiffness and smooth casing helps in threading it through the harness.
> I used the old coax as a "puller." Cut the old coax from the diode load
> terminals, and solder its braid to the braid of the replacement. Keep
> the junction as compact and smooth as possible so that it will pass
> through the harness easily. And you may need to use a lot of silicone
> spray to lubricate the harness and the replacement coax as you thread it
> through. You will need to loosen or temporarily remove any cable
> clamps, and some, but not all of the lacing and insulating sleeves may
> need to be removed to facilitate movement. Needle nose pliers, good
> eyesight and a lot of patience pushing and pulling are also needed.
IF deck tips                                     page 100

> Alternatively you can remove all lacing, replace the offending coax, and
> then relace the harness with new lacing or tie wraps. After getting the
> new coaxes into the harness and the ends positioned where they need to
> be, you will need to make the connections. This is easy at the diode
> load terminal points and the limiter switch at the front panel. But
> there are connections at the IF module connector that must be done
> also. You will need to remove the cover from the IF module connector
> and replace the connections there. In my case, I chose to replace all
> coaxes related to the IF module connection to the diode load terminals
> and from there to the front panel switch. My receiver also had the
> diode load test point on the front panel so this had to be accommodated
> as well. All in all, about a 2 day job, 2 hours per day for me. Just
> be sure it's not a bad capacitor etc. first, to avoid this cable repair
> if you can.
Date: Mon, 28 Jan 2002 07:27:44 -0500
From: Barry Hauser <barry@hausernet.com>
Subject: Re: [R-390] Popping noise problem

Well, that reminds me ... of someone on the list who's always reminding us to
check the nuts 'n bolts on the chassis and modules -- particularly the ones on the
tube sockets. Apparently the lightest corrosion between these screws and the
modules can cause breaks, high resistance connections or intermittents in
grounds. This might be related to the problem disappearing after the rig warms
up fully. The fix involves going over all the tube socket mounting screws with a
screwdriver -- loosening and tightening.

To that I'd add checking under the hoods of the multiconductor connectors,
particularly the large rectangular ones on the audio and IF decks.. The cables
stiffen up with age, the strain reliefs are not fully effective, and when you go to
unplug them, leads and shield braids can snap or crack. As I've mentioned
probably a half dozen times already -- I had a non-A where the main tie point
ground inside the large AF deck plug cover was broken -- just a buss wire
wrapped around all 12/13 braids goint to a single terminal (13, I think ;-) The
cable going to that plug tends to droop down below the chassis and get jostled
when you move it around.

Look for stuff like that. You might have to dumb down to find this bug.
From: "Jim Temple" <jetemp01@athena.louisville.edu>
To: <r-390@mailman.qth.net>
Subject: Re: [R-390] Popping noise problem
Date: Mon, 28 Jan 2002 09:14:27 -0500

Adding to Barry's list, be sure to carefully check the ground that is anchored by
T207 under the RF deck. When I cleaned and tightned mine, the rig "sprang" to
life. This is one that is not anchored by a tube socket screw and has several caps
and resistors attached.
IF deck tips                                     page 101

Date: Fri, 01 Mar 2002 14:46:12 -0500
From: Al Solway <beral@videotron.ca>
Subject: [R-390] IF Subchassis Resistor Value R-390

Need help with a resistor value. The installed resistor, R554, is 470 Ohm, 1 watt. It
measures 800+ Ohms so it needs replacing. My problem is that the schematic
indicates that R554 is 2200 Ohms. What is the correct value? This is the original
resistor, no signs of desoldering in the entire IF Chassis except for the BFO

Radio Info.
  R-390 Collins                                IF Chassis. Collins
  Serial No. 2113                              Serial No. 2571
  Contract No. 14214-PH-51-93
From: "Walter Wilson" <wewilson@knology.net>
Subject: Re: [R-390] IF Subchassis Resistor Value R-390
Date: Fri, 1 Mar 2002 20:53:14 -0500

The following was stated in Hollow State News #36, page 5 [Metz]:

"R554 coming off Z503 is schematically 2.2K. In four IF decks, the installed value
was 470 ohms (and looked original). I temporarily removed this resistor and
used a substitution box to experiment. It seemed that the 470 sounded much
better than the 2.2K or any other value for that matter."
Date: Fri, 01 Mar 2002 21:14:06 -0500
From: Al Solway <beral@videotron.ca>
Subject: Re: [R-390] IF Subchassis Resistor Value R-390

Well the consensus is that the R554 should be 470 Ohms. The out of spec R544,
800+ Ohms has been replaced. I thank you all for the response. What a great
bunch you all are. When I get the radio working I will let you know what, if any
problems I have with the AGC.
From: "John KA1XC" <tetrode@worldnet.att.net>
Subject: Re: [R-390] IF Subchassis Resistor Value R-390
Date: Fri, 1 Mar 2002 21:56:13 -0500

I've only seen the 470 ohm 1 watt in the several 390 IF decks I've worked on, and
other folks on the list have told me the same. Maybe this little piece of info could
be developed into a secret password or something to identify the 390 owners
from the 390A owners.
IF deck tips                                     page 102

From: "Jack Antonio" <dia@dia.reno.nv.us>
To: <r-390@mailman.qth.net>
Date: Sat, 2 Mar 2002 22:26:12 -0800
Subject: [R-390] Mech filter question

I just woke up one of my R-390As after a long nap, and it appears the 2 kc filter is
dead, nothing on the .1, 1 or 2 kc filter positions. Wiring appears OK. Filter
worked OK last time I used the radio, looks like this was a shelf failure. Question
number 1 is this: are ohmmeter checks on the mech filter input and output
terminals dangerous to the filter? I checked my ohmmeter on the Rx1 scale, and
into shorted leads, it puts out 50 mA, which seems like it might be too high for
the mech filter. The higher ranges put out less current, which brings up question
number 2:

What should the resistance of the input and output coils be? And yes, C-553 has
been changed.
Subject: Re: [R-390] Mech filter question
To: r-390@mailman.qth.net
From: "Roger L Ruszkowski" <rlruszkowski@raytheon.com>
Date: Tue, 5 Mar 2002 17:18:49 -0800

Jack, Did you get some direct mail back to help you with the filter. I did not see
any thing posted on the reflector. Use the Hi range (less current) and measure
the ins and outs, Compare them to the 4 or 8. All should have about the same.
Most filters do not just pop open. Look for a switch wafer that got oxidized.
Look for a spider web with under the deck or under the cover.
Look for some crud shorting the trimmer cap.
Date: Sun, 21 Apr 2002 14:33:12 -0500
From: David Medley <davidmed@sbcglobal.net>
Subject: [R-390] [R390] FS R-390 assemblies

I have the following R-390 parts for sale. Condition as noted.
1. IF decks. Complete without tubes or shields. Not tested $120.00
2. Audio/VR decks. Complete with tubes, inc 6082s. Not tested 50.00
3. Power Supply units. Good transformer but need some rewiring 25.00
4. Sets of two large knobs. Recently powder coated. Clamps missing 50.00

Will ship CONUS at buyers expense. Dave
Date: Sun, 21 Apr 2002 16:10:02 -0700 (PDT)
From: "Tom M." <courir26@yahoo.com>
Subject: Re: [R-390] Make your own R-725 was: FS R-390 assemblies

Note to project types who wanted to roll their own R-725. Dave has the coveted
R-390 IF decks.
IF deck tips                                     page 103

Date: Sun, 5 May 2002 22:58:08 +0200
From: federico.baldi@virgilio.it
Subject: [R-390] =?iso-8859-1?Q?MICRODIALS=20FOR=20R=2D390A/URR?=

I'm searching informations and if is it possible photos about MICRODIALS, a
sord of knobs with an digital mechanical counter inside, that I heard were
applied instead of BFO knob on R-390A/URR employed by NSA. I found a box
with five of this knobs. Any help very appreciated. Federico BALDI
From: "Greg Werstiuk" <greg_werstiuk@msn.com>
Subject: RE: [R-390] MICRODIALS FOR R-390A/URR
Date: Sun, 5 May 2002 15:37:38 -0700

I expect these were a "turns counting dial" as used with potentiometers for many,
many years. Some models are still in production. These are sold(but not
necessarily manufactured) by multi-turn potentiometer vendors such as
Vishay/Spectorl, Bourns and B I Technologies (formerly Beckman Instruments).
Bourns offers an embedded counter style such as you describe:


An alternative (counter is above the knob) is the Model 15 from Vishay/Spectrol
which can be found here:
From: "Bob Tetrault" <r.tetrault@attbi.com>
Subject: RE: [R-390] MICRODIALS FOR R-390A/URR
Date: Sun, 5 May 2002 23:23:51 -0700

They were used, as I understand it, not necessarily by NSA, for RTTY reception
and allowed precise settability. Others here on the list may know more about
them. They were a generic type of multi-turn knob and the full range of their
adjustment was not usable by the BFO. Have one and don't use it for my
From: "John Saeger" <john@whimsey.com>
Subject: Re: [R-390] capacitor analysis
Date: Sun, 2 Jun 2002 15:39:52 -0700

> Mine has had a pesky AGC problem which was very intermitent. On strong
> local stations all of a sudden I'd loose AGC action.... voltage would drop
> on the AGC buss from -9vdc to -4-6vdc and heavy distortion until the gain
> was backed off. Then it would stay like this for a while and suddenly
> return to normal.
> Finally tracked down the problem Friday to a bad 4 Kc filter that when it
> got heated up would short internally and screw-up the AGC line. When it
> cooled a bit it was ok......
IF deck tips                                     page 104

I haven't measured the voltage on the AGC bus, but this is almost exactly what
mine is doing. I get a drop in carrier level with a lot of distortion, and a sudden
return to normal. On strong local stations. But it doesn't seem to depend on
which filter I have switched in. And thanks to everyone who has posted on the
capacitor subject. Interesting food for thought.
From: "Scott, Barry (Clyde B)" <cbscott@ingr.com>
Subject: RE: [R-390] Carrier balance pot adjustment
Date: Mon, 3 Jun 2002 07:58:08 -0500

>There was a discussion a few months ago about making a few changes to
>the carrier pot adjustment to make it less critical and easier to set.
>One of the changes consisted of a resistor change and a wiring change.

Replace it with a ten-turn wire-wound pot. Works great.
From: David Wise <David_Wise@Phoenix.com>
Subject: RE: [R-390] capacitor analysis
Date: Mon, 3 Jun 2002 12:15:06 -0700

> suspect the problem is here. When the radio flakes out, the
> carrier level drops. But it doesn't happen very often. .................

Does it drop on all bandwidths, or only one? On my 1954 Motorola, the level
was low on 8KC. I traced it to the mica cap tuning that mechanical filter. In my
30 years (on and off) of restoring vintage radios, this was maybe my third bad
one. Micas are pretty good, but you should not trust them blindly. Those of you
with newer decks with trimmers: what's the temperature coefficient? NPO,
N750, something else, or unmarked? (How about the other trimmers? The
manual doesn't say. It may not be important. I'll take a peek
tonight.) Mouser carries a bunch of trimmers, with various TCs. If I switch over
sometime, I'd rather not figure it out by hand...
From: David Wise <David_Wise@Phoenix.com>
Subject: RE: [R-390] Carrier balance pot adjustment
Date: Mon, 3 Jun 2002 14:11:49 -0700

> There was a discussion a few months ago about making a few changes to
> the carrier pot adjustment to make it less critical and easier to set.
> One of the changes consisted of a resistor change and a wiring change.
> Can anyone provide me a copy of the messages?

The mod you're probably thinking of is mine. I posted instructions, but I couldn't
find them in a recent search of the archives. I reconstitute it here, except I can't
remember the wire colors.
IF deck tips                                   page 105

Get the schematic in front of you. The original connection is, V504 cathode via
R524 to meter, wiper, R537, and CW end. CCW end to ground. Other end of
R537 to ground.

My connection is, V504 cathode via R524 to wiper. CCW end to ground. CW
end to meter and R537. Other end of R537 to ground. Change R537 from 22
ohms to 15 ohms.

+ Smooth, almost linear adjustment range, with the operating point near
- Lower V504 gain (trivial, less than R524's 10% tolerance).
- More gain variation as you work R523 from end to end (trivial, *less* variation
       than before, when near the setpoint).
- Smaller reading on MGC overload. (Unimportant, overload is yes/no, not
~ Smaller full-scale reading.

  (Intentional; mine read high before. To change it, tweak R537. Smaller value
gives higher FS. 5.6 ohms is approximately original but puts the setpoint all the
way CW. Still smooth though!) Everybody seems to to have an opinion as to
how this should be fixed, and I'm no exception. My engineer's intuition says that
this is the "sweet spot". It's how they should have done it. I don't know how well
the R-390's carrier pot works. I expect it is fairly linear, but it might have a
coarse granularity. If so, you could change it to 100-ohm carbon and apply my
mod, and you'd get the same good result.
From: "John Saeger" <john@whimsey.com>
To: <R-390@mailman.qth.net>
Subject: Re: [R-390] capacitor analysis
Date: Mon, 3 Jun 2002 22:00:29 -0700

> Does it drop on all bandwidths, or only one?.................

So far the symptoms are the same at 16kc, 8kc, and 4kc bandwidths. I haven't
spent much time listening at 2kc bandwidth (yet). Michael Melland had
suggested that it might be one of the filters themselves causing the dropout.
That a short in a filter could cause a problem when listening at a different
bandwidth. I was hoping to get some different symptom at some particular
bandwidth if it was something like that. For example if it's the 4kc filter shorting
out, I might expect the signal to drop out completely when listening at 4kc, but
that hasn't happened. It's just a decrease, not a complete dropout. I still need to
test the 2kc bandwidth more though. I have noticed that the 1kc and .1kc
bandwidth positions don't seem to do much in the way of narrowing the
bandwidth, the signal level just decreases when I select one of these positions.
Maybe this is another reason to worry about C501. I don't know. I don't really
understand how this circuit works. The book says that C501 is a coupling cap
when using 2, 4, 8, or 16kc bandwidths, but it's something different when using
.1 or 1kc. Maybe its part of some kind of resonant circuit. Maybe it's gone out of
IF deck tips                                     page 106

From: David Wise <David_Wise@Phoenix.com>
Subject: RE: [R-390] capacitor analysis
Date: Tue, 4 Jun 2002 14:45:23 -0700

> So far the symptoms are the same at 16kc, 8kc, and 4kc bandwidths. …

The problem's not the filters, then.

> ....it might be one of the filters themselves causing the dropout. ................

Unused filters are out of circuit, unless the bandwidth switch is messed up. See
the Y2K manual, page 5-48. By the way, there's a typo on that page that could
confuse your understanding of C501's role. There's a dot missing. The bottom
end of C501 (which goes into Z501) also goes to V501 pin 1. In 2/4/8/16, C501
acts as a short around Y501, completely overshadowing Z501 and C520. At 1KC
bandwidth, it is out of circuit. At 0.1KC, it effectively bridges R503 across R502,
reducing the Q-spoiling resistance in series with C503. (C503 in series with R502
or R502|||R503 is in parallel with C524 and tunes L503.) This part of the IF
deck is shown correctly on page 3-13.

> I have noticed that the 1kc and .1kc bandwidth positions don't seem to do
much in the way of >narrowing the bandwidth, the signal level just decreases
when I select one of these positions.

If you apply 1KC or 0.1KC bandwidth to an ordinary AM signal, the sidebands
will be almost completely eliminated. The treble and midrange are gone, leaving
only bass, which the R-390A's internal audio amps are very short on, so if you're
listening through them, you won't hear much. If you put a hi-fi audio amp on
the Diode Load output, you'll hear the bass part of the program at the same
volume as before. For 1KC and 0.1KC, use CW or an unmodulated carrier and
go by the carrier meter reading. I seem to remember someone on this list
finding that his L503 was open. It seems to me that that would degrade
1KC/0.1KC performance. I can't remember when I last saw a bad ceramic cap.
From: David Wise <David_Wise@Phoenix.com>
Subject: RE: [R-390] capacitor analysis
Date: Tue, 4 Jun 2002 16:10:48 -0700

> > Unused filters are out of circuit, unless the bandwidth switch is messed up.....
> Now I'm really confused. My radio is being repaired/refurbed............

Well, you're not the only one. My bad. Unused filters are not in the *signal*
path, but they are still on the AGC line. Your diagnosis has not been disproven.
If you aren't up to paying for a replacement filter, you might be able to rewire
the bad one in a shunt-fed arrangement on the secondary, where a blocking cap
prevents it from grounding the AGC line, and you add a resistor for grid return.
The resistor could be oh I don't know maybe 100k. You'd still get noises as the
IF deck tips                                     page 107

filter went through its intermittent shorting regime, but the AGC would stay ok.
To check your diagnosis, I'd disconnect the filter secondary return bus from
AGC and ground it. This removes AGC from the 2nd IF, so you might want to
back off the RF gain during the test. If the problem goes away, you've
confirmed it's a filter. Then it's a simple process of elimination.
From: "Michael Melland" <w9wis@charter.net>
Subject: Re: [R-390] AGC problems
Date: Wed, 17 Jul 2002 15:19:33 -0400

Your problem sounds very much like the one that plagued my R-390A. The
cause of my problem was eventually found to be an intermitant short in the 4 Kc
filter. My 390A would start out with good audio and agc but when it warmed up
the audio would distort until I turned down the rf gain... obviously no agc action
was present. I also found the agc voltage to swing way low when this occurred.
Sometimes after some minutes audio would improve and agc would return to
normal. It was discovered that when the filter heated up as the radio was on it's
internal components would expand/contract and short to the case of the filter
grounding the agc voltage. Since all the filteres are, I believe in this circuit, it
could be any filter that is bad. The usual suspect seems to be the 4 Kc filter as I'm
told it was generally the most fatigued due to use.
Date: Wed, 17 Jul 2002 15:20:03 -0400
Subject: Re: [R-390] AGC problems
From: Thomas W Leiper <twleiper@juno.com>

You're right. You've got a leaky cap(s) somewhere on the AGC line. If you so
much as show a picture of a ten meg resistor to that line it will bury it's head in
the ground. You also may be missing the jumpers on the back panel or, least
likely, your AGC amp is weak. Finally, there is always the chance that the radio
simply doesn't like you, and would work perfectly for somebody else, like Barry
the Beggar.
Date: Fri, 09 Aug 2002 09:55:05 -0400
From: rbethman@comcast.net
Subject: [R-390] IF deck question

I have an older R-390A, a 1952 Collins contract, S/N 252. The IF deck is S/N 35.
It was only brought up to "MOD 1". It has no variable capacitors to tweak the
filters into line.
   1) Should I leave it that way and just take my chances with the filter
   2) Or should I try and scare up eight of the buggers and modify it so that I can
bring them right in on the money?
    3) If the latter, does anyone have a source of these critters?

I'm ready to start bringing it back to life, and want to lay out the course of
events. (Now if I can only find L501 that I scrounged to replace the one with the
broken slug.... Where oh where did I put that thing.........)
IF deck tips                                     page 108

Subject: RE: [R-390] IF deck question
Date: Fri, 9 Aug 2002 11:05:34 -0700
From: "David Wise" <David_Wise@Phoenix.com>

If I saw reasonable gain out of the deck, I wouldn't bother. Unless you're a
stickler for historical authenticity (in that case, you wouldn't put them in in the
first place), you can use any trimmer that covers the range and fits in the
available space. It won't be just a trimmer; the capacitance needed is too large.
Instead, it will be a fixed cap paralleled by a trimmer. I don't remember the
values, but they're in the manual. The manual doesn't say what the trimmer TC
is; probably NPO. I would probably compare an NPO to an N750 and pick the
one that stayed on the best. Mouser sells a variety of trimmers in various TCs. I
used a couple to redo my PTO's compensation; one NPO, one N1500, and turn
one up and the other down until the drift was minimized. By the way, changing
the total capacitance modifies the gross linearity, bowing the curve up or down
in the middle. Some of you might be able to avoid a linearity adjustment with
that trick.
Date: Fri, 09 Aug 2002 14:15:47 -0500
To: "Dallas Lankford" <dallas@bayou.com>
From: Death to Spammers <cv591a@bellsouth.net>
Subject: [R-390] St.J radios...long long long msg

>I wouldn't buy an R-390A from Fair Radio or anybody else unless I was certain
it did not come from the government auction at St. Julian's Creek Annex, VA.

I have to agree with you. Nasty nasty. Sad, too.

>A couple of years ago when the SJC R-390A's were hot items,..... Here are a few
of the things I remember from his discussion. Stainless steel screws rusted (not
surprising). This, of course, could make repairs more difficult. Yellow wrap
capacitors coming unwrapped. Well, that's not too tough. Replace the
capacitors. Coil windings in the shielded transformers of the RF deck starting to
come unwound. I don't know how you would fix this. His conclusion (not mine)
was that this RF subchassis was unsuitable for use in an R-390A.

I did some searching and found some of them. I seem to remember more. There
were several threads on the prospects of rebuilding one without future

(Begin Message 1)

Subject: Re: [R-390] New Owner
Reply-To: Nolan Lee <nlee@gs.verio.net>

>So, if someone got an R-390 A in their Christmas
>Stocking................ (I can dream, can't I?). Let's say a St.
>Julian's Creek victim. What would be the best first thing to do with/for it?
IF deck tips                           page 109

Rip it apart for parts. I've seen a couple of radios from there. Too many "little
things" damaged by the elements. You'd be looking at hundreds and hundreds
and hundreds of hours of work to bring them up to the level of a radio that'd
only cost you a couple of hundred dollars more in the first place. I don't make a
tremendous salary, but my spare time is worth a hell of a lot more than $0.51 an
hour. They're good for parts. If I could find a couple of them local for ~$100.00
each, grab 'em for spares. Don't get me wrong, I don't have a problem with
pumping tons of hours into a receiver. I just did one and am still working on a
second one. BUT, I started with two clean receivers. I can't see doing this with
something that'll always show the physical and emotional scars of sitting in the
rain and snow and sun for a couple of years when you can start with a much
nicer radio for a couple of hundred dollars more. Let's look at it from another
perspective. It's kind of like deciding that you want to build and drive a nice
looking, good running 1958 Buick Limited because you worship chrome and
they were cooler than The King (Elvis). Where's the first place that you'd look
for one to restore? Well, let's see, Otis, down at the local wrecking yard has one
that you can have for $125.00 dollars and $50.00 dollars freight, I mean a $50.00
wrecker bill to get it home. Best of all. you've got a couple of hundred dollars in
mad money that you picked up cutting pulp wood that the old lady doesn't
know about. ROAD TRIP! Load up the dogs in the truck, take a bottle of Rebel
Yell with you, and hit the road! HEEEHa! After 14 miles of dirt roads, you're at
Otis's place. "Out back of the tire pile", slurs Otis. You wade thru saw briars and
fight off swarms of mosquitoes, shoot two copper heads, and suddenly, there it
is! An aura of fire dances around it as the chrome reflects the sunlight into your
bloodshot lust filled eyes while the 4 foot tall briars rustle seductively in the wind
and the cicadas make the sound of Summer time love. Here Otis!, take the
money bubba, I gotta have it! Tow it out to my place and drop it next to Ma's old
burn out trailer. No, the first one.... Well, after you and the dogs and the car are
home, Otis is gone, and the Rebel Yell wears off, you eat a half a handful of BC's
to kill the headache and you ease over to it to evaluate your new "project".

It sat out there at Otis's place a few years after the courts released it. They never
did find the guys head or right foot, remember? Well, after setting here soaking
in the old UV rays, rain, dew, and snow, for a few years, the stench of death and
the blood stains are all gone. The chain saw cuts in the upholstery are still there
though. Gonna have to fix that.... The chrome still shines, and now, it's all yours
and you're now a full fledged member in good standing of the Cult of the '58
Buick Limited! Life is good bubba! It's had a few dozen other's like it stacked on
top at different times, and the roof is mashed in about 6 inches and the doors
won't open, but hey, it's tough, it's a 58 Buick and it's cooler than The King
(Elvis)! Besides, look at all of that chrome.... Six months ago, Otis's brother in law
was drunk and foolin' around on the fork lift after his wife (the gal with the big
hairdo) left him, and he accidently rammed a tine thru the grill, taking out the
radiator, cooling fan, water pump pulley, water pump and the upper generator
bracket. There's a few holes in the left fin where Otis Jr (product of Otis and
his 1st cousin Myra) sighted in his rifle one year. That boy never was what you'd
call "right". Most of the glass and various lenses are either missing or broken. The
numbers are peeling off of the odometer. The battery froze a few years ago and
IF deck tips                             page 110

ruptured, leaking electrolyte all over the inner fender and radiator support and
ate a hole big enough for a possum to climb thru. All of the tires are flat, two
wheels missing, and the two that are there are wrong. Whoa! Look at all of
those old snake skins on the engine. Cool! The deck lid and the intake manifold
and cylinder heads are missing too. What the hell, 58 Buick Limited deck lids are
common as dirt and so are the high compression heads for the 300 hp version of
the 364 cubic inch Buick engine. Oh, oh, the carb is gone too. ;-( Not a problem,
someone on the R_390_'58_Buicks_Cooler_Than_Elvis? reflector might have
some for sale. Oh, I almost forgot. The back seat and carpet has been the home
and breeding place of 17 generations of watch dogs for the wrecking yard. What
the...is that?...no... why yes, yes, I think that it really is, it's dog fur carpet bubba!
Damn, life sure is interesting at times! No thanks! I'd rather pay a more money
initially and buy one that's been sitting in a barn for years, and has all of it's
original innards after the little old lady that drove it into to town once a month,
went insane from watching game shows and drinking fluoridated water, and
committed suicide and was eaten by little Fluffy and the other 41 cats.

Your mileage may vary. If you're ever in this neck of the woods, I can fix you up
with Otis's 1st cousin Mrya. Since she got that new glass eye, the upper plate, and
the make over, she looks pretty hot...

nolan        CAT, the other white meat!
(Begin Message 2)

Subject: Re: [R-390] St. Julian's Creek radios
Reply-To: Nolan Lee <nlee@gs.verio.net>

At 06:42 PM 11/2/98 -0500, you wrote:

>Nolan, you are fogetting about the character of these
>radios. These receivers have been all over the world
>and served as soldiers for the good old USA, they deserve
>some respect.

I'm immune to that aspect of it. They're machines, nothing more. In the mid
1970's I worked for a division of Southern Scrap down in New Orleans. I had a
crew that averaged about 6 guys working with me. One of my jobs was to see
that all of the electronic gear that was worth anything, stripped out of two USN
WWII cruisers (Topeka & Boston) just ahead of the crews with the torches. BTW,
my Collins R390A is off of the USS Topeka.) The big dollar items like the guided
missle systems, fire control systems, etc. had priority. Most of the rest of the stuff
was just considered as obstacles impeding higher profits. I've cut up, destroyed,
burned, shredded, and smashed enough history to last several lifetimes. I've
taken sledge hammers and fire axes to stuff to get it out of the way so that I
could get to something that needed to be removed when I didn't have a fire
wrench (torch) handy and I dind't feel like using handtools. Sometimes we just
beat on stuff for the hell of it. "Hey! Bet you a dollar that I can knock that audio
amplifier off of the bulkhead with only two licks". On a side note though, I did
IF deck tips                           page 111

haul truckloads of RTTY gear and other stuff, in the form of TTY terminals, FSK
converters, etc. out of there that I gave away rather than see it run thru the
shredder. It cost me about 3 cents a pound to do this. :-) I still have a few pieces
of it. This was where I got the dozen or so R390A SSB converters that I once had.
Three cents a pound. :-)

>I own several, and by the time you go all the way through
>them, it's not that much more work. They may not pass for
>bright shinny new ones, but these things will still blow
>the doors off of any rice-box/sand-box SWL receiver.

Sure they will. It's just I'd rather start with something that's in better condition.
The two St.J R390A's that I looked at had set outside long enough for the digits
to start falling off of the counter and the color traces on the chassis harness to
fade away. I have to question the viability of the RF coils and forms, the IF coils
and forms, the PTO, the potentiometers, the switches, the UV damage to the
chassis wiring insulation, etc. before I spend hours and hours of my time
restoring it. What will it be like, electrically, ten years from now? Twenty years?
I generally keep stuff a long time and look at it from long term perspective.
They're well worth the ~$125.00 dollars that they sell for just as a source of parts.
Hell, the mechnical filters in the IF deck alone are worth the purchase price.

>It's neat to make a silk purse out of a sow's ear now and then.

Some people would probably find the '58 Buick Limited that Otis sold, an
enjoyable challange. I wouldn't. ;-)

>Sound's like Nolan may have ate a little too much
>CAT meat. Burrrp... It's gotta be well done...

With pecan sause.... <grin>

>In my opinion, the St. Julian's radios are worth more than
>"a just driven on Sundays by an old lady" R-390A.
>This is because of the history behind each one of them.
>When they are gone, there ain't gonna to be no more.
>These receivers are world class, if they could only tell
>us where they have been and what they have been through.

I was originally in awe of the R390A receivers when I saw my first one, but then
something happened that really changed my outlook on them. Another thing
that the division of Southern Scrap that I worked for did was dabble in the old
GSA auctions. We bid on and won hundreds and hundreds and hundreds of
R390A's back in the mid 1970's. Back then, all of this stuff was stored in
warehouses and not exposed to the weather. They all had the meters back then
too unless they'd been robbed for parts. At the time, a good working R390A
could bring close to $700 at the retail level. This is when a new fullsize GMC Cost
me 3654.81. I put $700 down and financed the balance for three years at $98.50 a
month. R390A's were not a cheap item back then. As a result, there was no
IF deck tips                           page 112

enviromental damage and they looked pretty damn decent. The nice ones that
were complete went first. We shipped most of those to Phil and George up at
Fair Radio Sales. Some went to other places, but truckloads went to FRS. At any
rate, as the pile of good complete ones got smaller and the pile of incomplete
ones got larger, I would strip modules out of some radios to be able to have
complete ones to ship. We also had a retail outlet and we'd keep it supplied with
clean working R390A's. After a while, a point was reached where we had dozens
and dozens of hulks that weren't worth the trouble to mess with. After I
grabbed a few extra goodies for spares for the R390A's that I had, they were
shredded bubba. I suppose that if I'd wanted to, I could have bought what was
left for .03 a pound rather than run it thru the shredder but I already had a few
good clean R390A's and enough spares to have lasted to today. :-) Picking thru
surplus R390A's 25 years ago was a lot different than today. :-)

>This is my two cents, whoever don't like it, <delete> please.

Cool! I did like it!
(Begin Message 3)

Subject: [R-390] St.J. receiver re-build
Reply-To: Nolan Lee <nlee@gs.verio.net>

At 10:59 AM 12/6/98 -0000, you wrote:

>I have had quite a job with the I.F. module. All of the 455 kHz I.F.
>transformers needed work, I think the rain had effected the glue that holds
>each end-cheek onto the coil former, with the result that the former would
>rotate and break the wire off.

I just finished gutting an RF deck out of a St.J. receiver for parts. I found a lot of
deteriation in the variable IF's and the RF coils in the RF deck due to exposure to
the elements. In addition, a lot for the tuning slugs were loose on their wires. It
ended up that about 20% of the plugin coils were out of spec and as a result,
were scrapped. All of the capacitors in them checked goo though. :-) My
comments on using the St.J. receivers as a restoration project have been voiced
here before and I won't go into it here. But, if you're going to re-build a St.J.
receiver, or any other receiver that's sat outside for a while, there are a few extra
steps that would probably be in your best interest, for the long term, to do: First,
I'd remove all of the variable IF and RF coils from the RF deck. Then, one at a
time, remove the metal covers and do an inspection and swab any film or loose
debris out of them, especially around the terminals, using a suitable solvent and
without wetting the coils them- selves. Some of the films (maybe oil washed
down from the rain from receivers stacked above it) can be conductive and give
false values when you do the resistance checks and probably would contribute to
signal loss. Measure the resistance of the coils and compare your readings to the
manual. Then, using a good sensitive bridge or VTVM that'll do >500 megohm
resistance or so, measure the resistance of the other pins to each other and to the
coil pins. If you get any reading here, you'll need to either track down the
IF deck tips                                     page 113

problem or replace the coil assembly. It doesn't take much of an oil residue on
the phenolic to give a 10 meg resistance reading. You may find lower than
normal readings on some of the coil windings due to failure of the insulation. ;-( I
had one RF coil that had leakage that turned out to be the trimmer capacitor. I
disassembled the cap and cleaned it and reinstalled it and the leakage was gone.
Oh, while you're at it, I'd give each of the trimmers a couple of three spins in
alternating directions to insure that the two little spring contacts are makling
good contact. Also inspect the coil forms and see if they are coming apart.
They're basically a flat spiral cut sheet rolled into a tube. I've seen them starting
to unwind on some of the coils of St.J. receivers. Redoping the coils and the
outside of the forms should prevent this and should stop any that has already
started from getting worse. I'd suspect that this will help the receiver to hold
alignment a lot longer. For the coils that meet resistance specs, I'd either bake
them in the oven at a very low setting for a couple of hours or place them in a
very dry (humidity) area for a few days or so and then redope the coils and
outside of the forms. Don't forget to check T207, T208, and the antenna trimmer
can on the RF deck. While you have the deck out, I replace the three paper
capacitors on the underside of the module and check the little nut mount paper
capacitor located near the 6DC6 tube. Another thing that's probably worth doing
would be to clean the bandswitch to not only make sure that the contacts are
clean but to remove any possible oil film. Any type of conductive film here can
cause a flashover and a carbon track to the shaft and render that switch section
unusable. The fiberglass ones seem to be more prone to flashover. These
switches were more of a problem than a lot of people think, evidenced by the
number of RF decks with mixed (ceramic and fiberglass) switch sections that I've
seen. ;-( I'd apply the same steps to the coils/switches/etc. on the crystal osc,
and IF modules.

nolan                                "Man, I'd kill for a Nobel Peace prize."
From: "Michael Young" <myoung76@bellsouth.net>
Date: Sun, 18 Aug 2002 21:41:31 -0400
Subject: [R-390] R390A IF chassis connector

Does anyone know the Amphenol number for J 512 on the IF chassis?
Comparing the schematics of the R390 and the R390A, they seem to be mirror
From: "Bill Smith" <billsmith@ispwest.com>
Subject: Re: [R-390] R390A IF chassis connector
Date: Sun, 18 Aug 2002 19:45:20 -0700

Don't know if this is helpful, but according to manual NAVSHIPS 0967-063-2010
(which has a parts list!) J512 is CONNECTOR, RECEPTACLE, ELECTRICAL: 20
male contacts (02660) type no. 26-806. Hope that is an Amphenol number. J512
on the 390 is a BNC connector. The 20 pin connector is J517 on the 390.
IF deck tips                                     page 114

From: "Michael Young" <myoung76@bellsouth.net>
Subject: Re: [R-390] R390A IF chassis connector
Date: Sun, 18 Aug 2002 23:25:33 -0400

Thanks Bill. That is the same AMP number as for the R390 IF module. Makes
my day. Is that NAVSHIPS document downloadable from somewhere?
Date: Mon, 19 Aug 2002 05:10:34 -0700 (PDT)
From: "Tom M." <courir26@yahoo.com>
Subject: Re: [R-390] R390A IF chassis connector

If you're asking about the main power connector, they are the same on the 390
and the 390A. In fact most of the functions are the same (but the modules are
not directly interchangeable).
Date: Wed, 28 Aug 2002 23:31:03 +0000
From: Philip B Atchley <ko6bb@juno.com>
Subject: [R-390] A tale of two IF decks.

Hello one more. Just pulled the IF deck from Dons R-390A. Even before pulling
it I "suspected" it was an "older" unit. It is, it's an early Collins IF deck. So, out of
curiosity, I put it next to the '67 EAC IF deck from my receiver. There are many
observable differences.

They are... 1. Most noticeable is the lack of filter trimmers on the Collins unit.
(2). The Collins appears to be "neater" in it's construction. I.E. The cable harness
is much neater, point to point wiring is neater also. (3) The Collins has
everything coated with that MFP crap which is going to make re-capping a
tougher job. (4) The EAC deck had nearly all capacitors of the newer type, I.E.
Yellow Aerovox and metal/glass. Only one "Brown beauty". The Collins is full
of the BBOD's

I believe this is an example where I'd take the EAC over the Collins every time
as it has all the updates.
Date: Fri, 30 Aug 2002 16:57:55 -0400
From: rbethman@comcast.net
Subject: [R-390] A tale of two IF decks & READING the WHOLE passage

| > I noticed a couple of other differences between an early Collins IF - S/N 35
| > vs. a '67 EAC IF. The Collins Z503 and the like do NOT have holes in them
| > to allow adjustment. The early Collins IFs that I saw WITH holes, were
| > obviously NOT done at time of manufacture. It is easy to see that they were
| > drilled out later. They usually have "flashing" around them.
| > I am guessing, but it was probably done at a later date to align them.
| ++++       | This is covered in the manual!
IF deck tips                                     page 115

I would have to disagree with that. Specifically, the manual says "remove" the
covers that do not have holes - and "temporarily" replace them with the shop set
that are drilled (or punched), perform the alignment and then "replace" the shop
set with the original.
| The first step to doing an alignment is to punch holes in those cans.
So either it was laziness or failure to follow "written procedure" that resulted in
the holes.
Date: Fri, 30 Aug 2002 17:07:53 -0700 (PDT)
From: "Tom M." <courir26@yahoo.com>
Subject: Re: [R-390] A tale of two IF decks.

You didn't comment on the sheet metal differences. EAC applied for and got
approval to re-design certain decks so that they could be wired easier.
Date: Sat, 31 Aug 2002 22:19:04 +0000
From: Philip B Atchley <ko6bb@juno.com>
Subject: [R-390] Low IF gain problem

Yesterday I mentioned that I thought the R-390A I'm working on seemed to
have low gain, though it was hearing weak ones ok (It "hears" my sig generator,
AM modulated 50% at it's lowest setting of -127dBM just fine). However I
mentioned I thought the IF gain seemed low as indicated on the S meter, so I
checked it by inserting 150uV at 455kHz into J513 and tried setting the gain
control for -7VDC at the diode load jack (per the manual). The highest I can set
this for is 5.0VDC and with gain about halfway (where I set previous receivers) it
reads 2.9VDC in ALL bandwidth settings.

Question. Does the Lankford AGC mod affect gain any in this IF strip, perhaps
by loading it down (2 diodes across a couple resistors)? I've tried subbing tubes.
If I can get the IF gain up this receiver will be working just fine (did a
pareliminary alignment already). I may have to finish recapping don's IF so I can
sub it for troubleshooting purposes.
From: DCrespy@aol.com
Date: Sun, 1 Sep 2002 10:55:19 EDT
Subject: Re: [R-390] Low IF gain problem

The Lankford mod does make the AGC more "aggressive". That is it takes less
signal to get the same AGC action. Very strong signals are reduced more than
they were before the mod. Dallas noted this in one of his HSN articles. It is a
fairly obvious side effect. I have done three radios with the mod, and have not
experienced the problem you describe, however. The S-meter readings did not
change significantly, so I do not think it is the mod. Unless... My mods have
always been done with 1N4148 switching diodes. I suspect that rectifier diodes
and some older general purpose diodes may be a problem. I have run into this
on similar AGC mods on the R-388. Something to check?
IF deck tips                                     page 116

Date: Wed, 04 Sep 2002 13:32:53 -0400
From: Bob Login <jlogin@mindspring.com>
Subject: [R-390] AGC..Z503 stuck slug

Hi, Working on a 390A with low agc voltage. As 455kc signal is increased the agc
voltage goes from positive 1v to negative but take plenty of signal.

Checked everything in both RF & IF decks. All components looked ok. So tried
to peak Z503 and seemed to work but slug seemed stuck after a few turns. Put
some WD on threads and tried again with plastic tool...it broke off...really feel
bad about that! Any suggestions....or someone out there willing to part with a
From: "Bill Smith" <billsmith@ispwest.com>
Subject: Re: [R-390] AGC..Z503 stuck slug
Date: Wed, 4 Sep 2002 15:20:47 -0700

If you can get the pieces out, carefully put them back together again with super-
glue. Don't use much glue, and make sure they fit together as tightly as possible.
Properly repaired, the slug will be as good as new.
Date: Fri, 20 Sep 2002 03:31:22 +0000
From: Philip B Atchley <ko6bb@juno.com>
Subject: [R-390] Adjusting BFO Neutralization

When I finished the Langford AGC/BFO mods I needed a way to set the BFO
neutralization. Not having a scope or other way to look at an RF signal at the IF
output jack, I was having difficulty doing this. I even tried making an RF probe
for my DVM, using a Ge diode, not sensitive enough. THEN, it hit me. I had that
MilliVac RF MilliVoltmeter that was given to me (a real obsolete piece of gear). I
had to contrive a way to connect to the screw on connector since the probe tip
was missing. Once that was accomplished, Eureka! It worked and I was able to
set the neutralization. Even after who knows how many years since the last
alignment AND the Langford mods it only needed just a slight tweak. So, I guess
that no matter how ugly (and it is an ugly greasy green rack mount unit) or
obsolete a piece of gear is, it may still be of use in the home 'lab'.
From: "David Faria" <dave_faria@hotmail.com>
Date: Sat, 28 Sep 2002 14:01:53 -0700
Subject: [R-390] IF alignment Using Sweep Generator

Good afternoon list - just thinking abt the procedure that is going to be posted
so, here's a topic. There appears to be an IF frequency unique to each filter and
its not exactly 455khz. Do we align the IF for an average frequency that works
for all the filters or just for the filter we are going to mainly use? Does it make
any difference? Food for thought for those of us who are retired/bored and
looking for when the mil. procedure is posted. And if it has been posted and I've
missed it would someone please send me a copy.
IF deck tips                                     page 117

Date: Sat, 28 Sep 2002 15:04:40 -0400
From: Jim Brannigan <jbrannig@optonline.net>
Subject: Re: [R-390] IF alignment Using Sweep Generator

Unless one of the filters is way off frequency, the IF bandwidth should be broad
enough to accommodate the variances.

From: Rodney Bunt <rodney_bunt@yahoo.com>
Subject: Re: [R-390] IF alignment Using Sweep Generator

Tune the IF centre frequency for that narrowest filter you are using. The other
filters will be wider and the bandpass of the Xtal/mechanical filter will fall within
the IF. If the "narrowest" filter were to fall on the "skirt" of the IF bandpass, then
the IF gain would be lower as it would be at the edge of the IF, you would also
get considerable distortion on MCW.
Date: Fri, 04 Oct 2002 11:27:59 -0700
From: Tony Angerame <tangeram@lucent.com>
Subject: [R-390] Staggered IF Question
         I have a Capehart R-390a in truly excellent condition. It was apparently
stored in a closet shorthly after Vietnam. I've done a fair amount of recapping
etc but the radio plays great and doesn't appear to need an alignment with one
exception. I noticed that when I select the 4 kc and below filters the signal level as
indicated by the carrier meter decreases by about 5-10db. This is true for .1, 1, 2
and 4kc vs. 8 and 16. I swept the input of the radio at the selected bandwidth say
16 kc from my generator and noted about 6 peaks throughout the 16 kcs I swept
and noted proportionally less peaks for the lower bandwidths. So my theory and
my question is am I seeing the peaks of the six tuned circuits in the IF (455)? Has
this radio been stagger tuned to produce a uniform bandwidth in the wider
positions? Is this why I notice a slight increase in gain when I select the wider
selectivity positions? I notice that the manual calls for a peak alignment of the IF
transformers.Seems to me this would cause a big "Hump" especially in the wider
positions and I'm better off with what I've got.
From: "Philip Atchley" <k06bb@elite.net>
Date: Sun, 27 Oct 2002 03:20:00 -0000
Subject: [R-390] That R-390A "BFO Thingy"

Hello all. I use VERY sharp audio filters with my R-390a in the CW mode. While
my receiver is easier tuning than 'most' I've had it can still be a little difficult
sometimes to exactly set the tuning in the center of the Audio bandpass (my
present sharpest filter is 80 Hz but I have a much sharper one coming). I
sometimes like to tune my receiver where the desired signal makes it through
the filter and the undesired is off the slope of the filter, sometimes hard to do
with strong nearby carriers. I sometimes use the BFO to "tweek" the audio note a
tad but then have to reset it back as I use the 100Hz IF filter too. Resettability is
good, but could be better. Some of the 390A's I've seen have a little BFO vernier
IF deck tips                                     page 118

for setting the BFO. Are these good and resettable (seems like they would be).
Can they be retrofitted to a receiver that doesn't have one or is it a pain? And
lastly, are they available at reasonable cost? Can't get one right now but I'd be
interested in hearing what the group has to say.
From: "Bob Tetrault" <r.tetrault@attbi.com>
Subject: RE: [R-390] That R-390A "BFO Thingy"
Date: Sat, 26 Oct 2002 20:51:35 -0700
         They aren't verniers; they are still 1:1, and so their settability is only
marginally better than the front panel. IMHO
From: "Barry Hauser" <barry@hausernet.com>
Subject: Re: [R-390] That R-390A "BFO Thingy"
Date: Sun, 27 Oct 2002 01:54:13 -0400

I bought a couple of those odometer style BFO knob things a while back. As Bob
pointed out, they are not verniers -- 1:1. The idea may have been to improve
reset-ability, but they introduce some slop. Some may be worn inside and the
action is rough. They are not difficult to fit, but I doubt if it will help you. Best
bet is to find the small "combination lock" style verniers -- the ones you see on
some scopes and other test equipment, though I don't know if they use a 1/4" or
1/8" shaft size. They usually also have a locking lever. That would give you
vernier reduction and an accurate scale for resetting. Not sure how they mount
up. Alternatively, there are those small inline vernier couplings which I think are
still available new from catalog sellers. It's possible they would just fit in without
drilling, but the existing shaft might have to be shortened. The ones I'm thinking
of don't have scales, though.
From: "Barry Hauser" <barry@hausernet.com>
Subject: Re: [R-390] That R-390A "BFO Thingy"
Date: Sun, 27 Oct 2002 13:16:25 -0500

Well, I think you're right on the small scope type verniers. Newark lists a bunch
of them. Here's one:

talog/product Detail.jsp?id=12F4498

-- 15 turns, but as I recall, I've always seen those coupled to a multiturn pot as
you point out. The business end turns 15 times around, or 11 for the other

But -- never say "ALL". ;-) There is a similar style, but larger -- 1.5 to 2 inches in
diameter which are true verniers with reduction. Mouser lists 3 of them. Here's
the link to the pdf page:

IF deck tips                                   page 119

These appear to be of the same style as the ones Radio Shack used to carry. I
may have one or two lying around somewhere. They provide an 8 to 1 gear
reduction. However, they mount up not by the front panel nut, but flush-mount
with 3 screws. They take a 1/4" shaft, but have a coupling with (as I recall) a
round head screw rather than a setscrew, so may need an oversized hole to
clear. Not sure how much play is available on the depth. One possibility to avoid
drilling 3 holes (arghhhh!) is to use 3M mounting tape. That's the stuff that's
sticky on both sides, thick and rubbery. It will hold for sure, but when the time
comes to remove it, it will probably take the paint with it. I seem to recall these
having a rotation of 270 degrees, roughly matching a typical pot. However, the
Mouser description says "calibrated for 180 degrees rotation" -- which should be
good for the BFO anyway. The last type I mentioned in my previous post was
truly a gear reduction drive, but I haven't found a listing for it. These were
simply a knob shaft, a drive shaft and a disk shaped "gearbox" in the middle.
(might have been a friction drive) No knob, no scale. Not sure how it mounted.
Used to be in all the major catalogs in the old days. Anybody familiar with
From: "Bob Tetrault" <r.tetrault@attbi.com>
Subject: RE: [R-390] That R-390A "BFO Thingy"
Date: Sun, 27 Oct 2002 09:14:47 -0800

They are ALL 1:1. They were built for multi-turn pots which were therefore
built-in verniers over the single turn variety. They all mount to the front panel
Date: Wed, 30 Oct 2002 20:14:29 -0600
From: Dave Metz <metzd@intelos.net>
Subject: [R-390] BFO question

I recently fired up a nice EAC A model that has been sitting on the shelf for a
couple of years. When I put it away, it had just been polished, cleaned, aligned,
and working great! It still seems to work fine except for the BFO. You cannot
turn it far enough CCW to get a zero beat even taking off the knob and gently
turning it to the left stop. (perhaps another quarter turn (if available) would zero
beat it at full CCW) So far the only thing I have tried is changing the BFO tube
but no change. Is there anything else except inside the BFO assembly itself that
could cause this? Any points would sure be appreciated.
From: "Philip Atchley" <k06bb@elite.net>
Subject: Re: [R-390] BFO question
Date: Thu, 31 Oct 2002 01:25:31 -0000

I'd suspect one of the capacitors in the BFO circuit has gone "belly up". Possibly
the mica unit that is directly connected to the BFO coil (don't have the schematic
in front of me right now).
IF deck tips                                     page 120

Date: Tue, 10 Dec 2002 08:23:26 -0700
From: Chip Owens <owens@atd.ucar.edu>
Subject: [R-390] Z-503 replacement & R-542 value

Some archive info on the value of R-542 suggests 470 ohms instead of the
original 2.2K-ohm value.I'm curious about this. How does decreasing the value
of a de-coupling resistor improve performance? The archive info is a couple
years old. What is the current thinking on the value of R-542? And what
performance improvement is achieved by decreasing it to 470 ohms? I'm
replacing Z-503 (the hard way) and since I'm in that part of the IF chassis I
thought I'd replace any out-of-spec component at the same time.
Date: Mon, 16 Dec 2002 13:44:46 -0500
From: Albert Solway <asolway@sympatico.ca>
Subject: [R-390] Soldering Fine Gauge Wire

To All, Some time ago there was a request on how to remove the the insulation
on fine gauge wire as used in IF Transformers. One of the responses was to use
an aspirin to remove the insulation. My question is, what is the procedure. Any
other techniques would also be appreciated.

The wire from L52, part of T1 in my SP-600, was broken. The remaining useable
length is about 0.5 inch to short to reach the terminal it goes to. A splice is
needed. I tried solder with only a flux and the iron without success.

The insulation is a high temp type and will not melt with the soldering iron. The
broken wire was most likely the original fault in the SP-600. I found it by accident
while replacing the BBODs.
Date: Mon, 16 Dec 2002 02:17:24 -0500 (Eastern Standard Time)
From: Helmut Usbeck <vze2gmp4@verizon.net>
Subject: Re: [R-390] Soldering Fine Gauge Wire

I've so-so luck with the aspirin technique, best bet seems to use a cheap aspirin
with no coating.

What I've been doing of late to tin small gauge wire on coils and toroids is to
puddle a blob of solder on the end of an iron and then run the wire though the
blob which burns off the insulation and tins it nicely after a quick wipe with a
From: "Bob Tetrault" <r.tetrault@attbi.com>
Subject: RE: [R-390] Soldering Fine Gauge Wire
Date: Mon, 16 Dec 2002 11:37:02 -0800

I've been doing the solder blob as Helmut describes for years.
IF deck tips                                    page 121

Date: Mon, 16 Dec 2002 14:34:14 -0800
From: Dan Merz <djmerz@3-cities.com>
Subject: Re: [R-390] Soldering Fine Gauge Wire
         Al, I've done a few repairs similar to your task . I never liked the "heat it
in solder until" technique - some coatings just are very resistant. I've gone down
to about #44 wire size - and I scrape the wire by holding a flat piece of metal on
one side and lightly scrape with a scalpel or xacto knife. You have to work
different sides of the wire so it takes a little time - it helps to have a magnifier.
Then when I've seen enough copper, I fashion a splice with small bare copper
wire wrapped on the two ends you want to join, #38 or smaller, and solder the
two joints. Fine tweezer help here. I've had very good success with this,
especially on transformer windings and rf coils.                               Dan.
Date: Mon, 16 Dec 2002 15:10:26 -0800
From: Dan Merz <djmerz@3-cities.com>
Subject: [R-390] BNC to MB adapter?

Hi, I need an adapter to take one end of a BNC jumper cable to type MB, ( the
small bayonet connector in a 390a). I believe this adapter is an Amphenol 47200
connector, like the i.f. output connector on the back of a 390a. I am going from
the BNC connectors on a 390 i.f. chassis (male bayonet/female pin) to the
corresponding two MB (female bayonet/female pin) cables on a 390a. I need
two of these adapters. Does anyone have a couple of these to spare, know where
I could find them, or know of another type of connector that will do the job
without altering the connectors on the 390a?                                      thanks, Dan.
From: Buzz <buzz@softcom.net>
Subject: Re: [R-390] Soldering Fine Gauge Wire
Date: Mon, 16 Dec 2002 20:19:46 -0800
         I have a small bottle of paint remover on my workbench. I just dip the
end of the wire in, wait a few seconds, then wipe the insulation off.
Date: Fri, 20 Dec 2002 12:46:21 -0800 (PST)
From: "Tom M." <courir26@yahoo.com>
Subject: [R-390] R-390, Low AGC Voltage

Group, I have a 390 with a low AGC voltage, runs about half of what my 390A
deck runs. The 503 coil works, AGC amp (V509) amplifies, rectifier rectifies, I've
changed numerous suspect caps, volts look OK, tubes are OK, and yet I still have
low AGC voltage. When I impose a negative DC voltage on the 3-4 terminals on
the back, the gain goes way down, so I know the controlled tubes are being
controlled. The radio plays OK except AGC action is not as good as expected. It
loses control on very loud stations such as BBC 5975. I'm thinking of running a
SS full wave bridge rectifier ahead of the tube rectifier to boost the rectified
voltage, i.e. send only negative volts to the 12AU7 rectifier instead of the AC
from the AGC amp output. Has anyone ever tried this, or otherwise have
suggestions about 390 AGC low level?
IF deck tips                                     page 122

Date: Thu, 02 Jan 2003 18:30:19 -0500
From: MURPH <rickmurphy1001@earthlink.net>
Subject: [R-390] Those pesky trimmer caps

Does anyone know where I can purchase the trimmer caps that are in the second
osc? I have two that are bad but am looking to replace them all. I might have to
resort to soldering substitutes under the deck. Gone are the days when one
could walk into the local electronics parts establishment and get this kind of stuff.
No where to be found here in Chas. SC.
Date: Thu, 02 Jan 2003 18:43:29 -0500
From: "Jim M." <jamesmiller20@worldnet.att.net>
Subject: Re: [R-390] Those pesky trimmer caps

If these are the ones in the xtal oscillator, American Trans Coil sells pulls from old
390-a's. They're on the web.
From: "Steve Hobensack" <stevehobensack@hotmail.com>
Date: Thu, 02 Jan 2003 18:52:35 -0500
Subject: [R-390] bfo problems

My r-390a has a slight hum when the bfo is on. Cw and ssb signals have a slight
"vibrato" sound. Cw notes are not clean and crisp with any setting of the mgc
level. I suspected one of the filter caps, but they are ok. The decoupling cap on
the bfo 150v b+ is ok , there is no cathode to filiment short.

I turned off the bfo switch, and injected a 455 khz carrier from my urm-26d
signal generator to pin 5 (plate)of the tube socket. I still had the hum with the
signal generator acting as the bfo. The radio sounds fine listening to a m
broadcast. Any ideas ??? Thanks
Date: Thu, 02 Jan 2003 19:01:40 -0500
From: Jim Brannigan <jbrannig@optonline.net>
Subject: Re: [R-390] bfo problems

I had a similar problem with a 75S-3B. It drove me crazy trying to find it......
It turned out to be a bad tube in the PTO.........
From: Llgpt@aol.com
Date: Thu, 2 Jan 2003 19:29:32 EST
Subject: Re: [R-390] Those pesky trimmer caps

Check with Chuck Rippel, at one time, he had a large supply of the trimmers......
IF deck tips                                     page 123

Date: Thu, 02 Jan 2003 19:50:02 -0500
From: Bob Camp <ham@cq.nu>
Subject: Re: [R-390] bfo problems

> My r-390a has a slight hum when the bfo is on...........................

My bet would be AC modulation of one of the oscillators. Most oscillators will
FM before they AM so low level modulation would only be apparent with the
BFO on. Going *way* out on a limb - check the PTO first.
From: "Walter Wilson" <wewilson@knology.net>
Subject: Re: [R-390] bfo problems
Date: Thu, 2 Jan 2003 20:27:47 -0500

As Jim said, check the PTO tube. But while you're in there, make sure the metal
L-shaped grounding strap that contacts the PTO shaft is making good contact.
This is the electrical ground for the PTO shaft, and should NOT have any
lubrication applied. If any is there, remove it. If the PTO shaft is not grounded
properly, the oscillator will warble.
From: "Kenneth G. Gordon" <keng@moscow.com>
To: "Steve Hobensack" <stevehobensack@hotmail.com>
Date: Thu, 2 Jan 2003 21:03:07 -0800

Substitue the HF oscillator tube and/or any heterodyne/conversion oscillator
tube. I have an HQ-110-C which did the same thing. BOTH the HF (tunable)
oscillator tube and the 2nd conversion (crystal) oscillator tubes had high cathode
to filament leakage.

My TV-2 said they were both all right. Cured it by substituting new tubes.
Afterwards, I found a service bulletin from Hammarlund that explained the
problem, which was apparently not uncommon.
From: DAVEINBHAM@aol.com
Date: Fri, 3 Jan 2003 15:59:49 EST
Subject: Re: [R-390] bfo problems

Back when I was in the Air Force 40+ years ago, they taught us that if the tube
tester says it's bad, the tube is bad. But if the tube tester says it's a good tube, it
ain't necessarily so. The " best" way to test a tubes is to temporarily replace it
with " a known good tube."
IF deck tips                                     page 124

From: Llgpt@aol.com
Date: Fri, 3 Jan 2003 16:06:26 EST
Subject: Re: [R-390] bfo problems

Well put Dave!! Tube testers are a useful tool when utilized properly. many is the
tube that tested good, but didn't work in a particular circuit, but did well in
another. Les
Date: Thu, 2 Jan 2003 22:26:27 -0800
Subject: Re: [R-390] bfo problems
From: ronald j deeter <k6fsb@juno.com>

I had a very similar problem tracked it down to a filament to cathode short on
the AGC rect tube V509. So look for a tube. substitution is the fastest way to
track it down.
Date: Sun, 19 Jan 2003 22:42:57 -0800
From: Dan Merz <djmerz@3-cities.com>
Subject: [R-390] Tightening shaft connection?

Hi, is there a good trick to tighten the bandwidth shaft coupler if the shaft
coming out of the i.f. chassis seems a bit small.

The shaft coupler worked ok on the 390a i.f. chassis but when I put the 390 i.f.
chassis in the 390a radio, the shaft seems a bit small for the coupler even when
tightened down pretty tight (gap closed).

More to come on the successful conversion of the 390 non-a i.f. to go in the 390a,
but I'm trying to solve this problem so I can change bandwidth without taking
the i.f. chassis out - it seems awkward to have to do that. I tried putting a 2 mil
shim sheet on two sides of the shaft in but that still didn't give enough purchase
on the shaft. Maybe there's a gritty substance that would help? thanks, Dan.

Date: Mon, 20 Jan 2003 06:59:03 -0800
From: Dan Merz <djmerz@3-cities.com>
Subject: [R-390] 390 non-a i.f. in R390a

Hi, I completed the conversion of a 390 non-a i.f. chassis to go in a R390a radio.
This follows the article of Tom Marcotte in Electric Radio Dec 2000 describing the

I found his article flawless in the detail given for point-by-point wiring changes
and thank Tom for writing the article and providing me a readable schematic for
the 390 non-a chassis and some other information on the R-725.
IF deck tips                                    page 125

I deviated slightly in a couple of cases to utilize some of the existing wiring but
this was just a preference on my part and amounted to the same connections.
Most of the wiring mod's involve converting the series connections for 25 v
filament supply used in the 390 non-a to the 6.3 volt connections required in the
390a, plus dropping the B+ voltage a bit. This is all explained clearly in his article,
along with the background for the R-725 radio which the final set emulates. No
modification of other parts of the 390a radio are required other than taking the
390a i.f. chassis out.

The conversion was done on a junker 390 non-a i.f. chassis sold on eBay and it
worked immediately upon putting it into the EAC 390a set, which brought a
feeling of relief since I had no idea what might be wrong with the junker chassis
and I didn't have a 390 non-a radio to test it in. One of the bigger tasks was to
make a cable adapter for BNC to mini-BNC, or MB, connectors for the two
inputs from the 390a r.f. chassis. Tom used two of the 390a i.f. output adapters of
the type on the rear panel of a 390a. I had trouble finding these, and I'd like to
thank Roy Morgan for his assistance in trying to get the relevant connectors
from The RF Connection - I opted not to use their MB female to BNC female
adapter because the two critical parts would have cost $20 each plus shipping and
I would have to make up two short BNC to BNC cables as well.

Instead I used some chassis mount MB connectors from Fair and made a small
aluminum box with the MB connectors on one side with RG 58 entering on the
opposite side, with a BNC connector on the outside end of the RG 58. I can't say
cheaper is better but it was a bit of fun and turned out well. If there is any
interest, I'll post the details of how I did that but it's not too complicated. I'd
recommend buying the RF Connection adapters unless you enjoy cutting and
bending metal like I do. I'm assuming the adapters from RF C look more or less
like the 390a back panel i.f. adapter.

I was quite impressed with the appearance of the 390 i.f chassis, though it's
much more crowded than the 390a i.f. chassis and not the easiest thing to reach
into with a soldering iron, even a small one. My first reaction on looking at what
had to be done was "ughh." As Tom advised, use any trick you can think of to
do the soldering. So when I finished the soldering, I felt I had done something
challenging and had not destroyed the beauty and function of the unit in the
process. I hope the next guy looking at it will find equal enjoyment with the
unit. This project took about 2 years to complete, most of that time looking for
the i.f. chassis after I read Tom's article. I got this chassis Dec 27 so it took about
3 weeks to round up the connector stuff and make the conversion after that.

I'll post my impressions once I test the set a bit more; I'm going to add the two
diodes ala Lankford and increase the bfo coupling cap. Thanks to all for earlier
comments regarding the connectors, Dan
IF deck tips                                     page 126

Date: Mon, 20 Jan 2003 20:42:57 -0800
From: Dan Merz <djmerz@3-cities.com>
Subject: Re: [R-390] 390 non-a i.f. in R390a

Hi Scott, an R-725 is more or less what I now have, though built by
contractors, and had the 390 non-a type i.f. in a 390a radio, and a couple of other
mods, one to improve PTO stability and an added 25 volt filament supply to
power the R-390 i.f. chassis.

The purpose was to eliminate the non-linear phase shift caused by mechanical
filters, which caused errors for direction finding equipment, and I guess to have
a current production radio at the time. The decision was made that was nearly
the same as the 390a otherwise, in the early 50's. Approximately 300 were made
according to Tom's article. I don't know more details of exactly how it was used.

Yes I did it for the fun of the project and to explore and perhaps enjoy the audio
characteristics of a 390 non-a i.f. , which is reported to be more pleasant to the
ear. Why not just use a 390? I don't have one and decided I would rather not
obtain one for now because of space and effort to get it going and the 390a I
have is a clean set - one 390 type radio seems to be enough so far. They are
somewhat inconvenient to casually move around from a behind-the-scenes
location and use when the fancy strikes you. Who knows what the future will
bring. I've been known to change my mind about such things,

I have several other types of communication radios competing for shelf space
where I can operate them so my decision was biased by that consideration. I am
pleased by the consideration that the chassis can be easily swapped in about 15
minutes, and either will work interchangably in the 390a radio. I can't think of a
reason to have this conversion if you already have a satisfying 390 non-a unless
you want to see if it will perform a little better, or are just very curious and like
the unusual.

Marcotte wrote in an earlier ER article about the R-725 he had at the time, April
1996: "How does it work? Quite well, just like an R-390, but with the
smoothness of the fewer gears of the R-390a gear train. It is actually more
sensitive than my all-Collins R-390 and R-390a, and has none of the ringing
caused by the mechanical filters in the R-390a." So that's my story and I may not
stick to it. If I missed some aspect that interests you, ask away, best regards,
IF deck tips                                     page 127

Date: Mon, 20 Jan 2003 14:31:42 -0800 (PST)
From: "Tom M." <courir26@yahoo.com>
Subject: Re: [R-390] 390 non-a i.f. in R390a

The R-725/URR is a modified variant of the R-390A. It has a special IF deck (95%
like the R-390 IF deck except it runs on 6V instead of 24V) called the Series 500
deck, which enables the 390A frame to be used in DF applications as with the
TRD-15. The R-725 also has a PTO mod to prevent hum. Motorola, Arvin and
Servo were engaged in making the new IF decks for dropping into existing
R-390A's, pressing them into DF service.

The new IF decks were not entirely new; some parts were salvaged from the
(now junker) R-390A IF decks that were removed. The R-725 has the nice sound
provided by the tuned circuit IF, arguably better than that of the 390A with
mechanical filters. Why not use the 390? Because I don't have one. The objective
of the project was to get better sound out of the R-390A, keeping the R-390A IF
deck available for hard core DX. There are no permanent mods to the 390A,
which was another objective.
Date: Tue, 21 Jan 2003 16:02:55 -0800 (PST)
From: "Tom M." <courir26@yahoo.com>
Subject: [R-390] R-725/URR Hum Bucking Transformer

Someone asked about this. In the original article about the R-725/URR, I wrote
that the extra transformer was for IF filaments. But then I got some info from
Servo which stated otherwise (mea culpa!). "A hum-bucking circuit has been
added to the R-390A/URR to improve performance. This modification places a
positive dc voltage on the filament of the variable frequency oscillator (vfo)
(V701) in the receiver, reducing the heater-to-cathode leakage of 60 Hz into the
signal." Further on the hum thing.

"The following modifications have been made to reduce hum.

(a) Open small enclosure at end of vfo unit and lift pin 3 of V701 from ground.
(b) Connect a 0.01-uF capacitor between V701-3 and ground.
(c) Connect V701-3 to J709-C. <==(this connects new transformer. Ed.)
(d) Connect P109-C to P121-E (filament return)
(e) Disconnect and dead-end wire (with tape) from P112-8."

End of Servo info.

ps The Servo info also indicated provision has been made for use of a dynamotor
for DC operation (anyone seen this?).
IF deck tips                                     page 128

From: Llgpt@aol.com
Date: Tue, 21 Jan 2003 19:31:01 EST
Subject: Re: [R-390] R-725/URR Hum Bucking Transformer

You forgot to add the original R-725/URR receivers had a MU-Metal shield
around the PTO. No mention was ever made of this in their (Servos) blurb, but
obviously was placed arounf the PTO to eliminate any spurious emissions from
the PTO that would/could have interfered with the DF'ing.
Date: Tue, 21 Jan 2003 21:43:21 -0800
From: Dan Merz <djmerz@3-cities.com>
Subject: Re: [R-390] Tightening shaft connection?

Tom, I might need that coupler. After making the Lankford diode additions and
a 47 pf cap to the bfo output, I discovered the coupler was actually broken on
the bandwidth shaft connection right near the nut so that is kaput - I guess I
didn't see this before and/or possibly over-tightened it to cause the break. I
also noticed the coupler on the bfo shaft is broken on the side opposite the
tightening screw but it will still clamp down enough to work. I remember
discussion of these being susceptible to breaking. I looked at one closely and it
looks like an anodized aluminum alloy - definitely non-magnetic material - so
I'm assuming aluminum. Has anyone made these out of brass or a material not
apt to do this. The fracture reminded me of season cracking of some brasses
which is a stress corrosion problem. High strength aluminum alloys can also
have this problem. I am quite curious about how these shaft couplers were
fabricated - does anyone recall anything about them?....... It's tomorrow now
and I decided to make my own couplers out of 6061-T651 aluminum plate that I
found in my garage - hopefully these will be better than the originals - they are
about half done - fortunately the hole is a standard size, 5/16 inch and
aluminum is almost like wood to saw, file and shape so it's not going to take
long. I expect these to be superior to the originals. Are the small size type more
suscetible to breaking than the larger ones - it appears to me they would be from
the shape?

Another problem as well. The bfo is not acting very nice now - if I turn it on
with say a broadcast station tuned in, the gain is reduced immediately to a low
level. I wanted to re zero it since I turned it some when I was working on the
circuit under the bellows. I don't seem to hear the bfo like I did before when it
was tuned off zero.

Do I have too much bfo getting into the agc circuit with the increased capacitor
(47 pf across the original 10 pf) I put in or is this the symptom of some other
problem? I explored this a bit to make sure I didn't fry the coupling caps when I
soldered but I don't think that's the problem. Is the adjustment of the
neutralizing cap critical enough to cause such a big effect. My first reaction was
to take the added cap out and see if good behavior returned.
IF deck tips                                     page 129

From: "Drew Papanek" <drewmaster813@hotmail.com>
Date: Wed, 22 Jan 2003 17:15:46 -0500
Subject: [R-390] R-725/URR Hum Bucking Transformer

...........original R-725/URR receivers had a MU-Metal shield..........

Mu metal is used for magnetic shielding and is often found encasing electrostatic
deflection CRT's in oscilloscopes. There it prevents trace deflection caused by
stray magnetic fields from 'scope's power transformer.

Magnetic shielding for PTO in R-725 would prevent FM-ing of PTO signal due to
transformer induced 60 Hz "permeability modulation". The aluminum PTO cans
would not provide magnetic shielding but would provide effective RF shielding
thereby minimizing the aforementioned spurious RF emissions.
Date: Wed, 22 Jan 2003 16:39:04 -0500
From: Jim Brannigan <jbrannig@optonline.net>
Subject: Re: [R-390] Tightening shaft connection?

Actually the problem with most AM detectors is too little BFO injection in
relationship to the IF signal. Of course these detectors are not build to filter the
increased BFO signal and it will get into the AGC.
Date: Wed, 22 Jan 2003 14:39:28 -0800
From: Dan Merz <djmerz@3-cities.com>
Subject: Re: [R-390] Tightening shaft connection?

Hi, my interpetation of Bob's comment was that the 47 pf caused too much bfo
into the detector for the agc - my goal in putting it in was to increase the level
needed for ssb, as Jim noted. I have now taken the 47 pf out and the set
behaves itself now as far as agc goes. Because I have to crank down the rf level a
bit, I'm thinking it could use a little more bfo but it's workable with the just the
10 pf. It's much better than it was before I put the 2 diodes in, so I'm happy with
that. For some reason (maybe I didn't want to take the bfo bellows out), I didn't
put the 47 pf in my 390a i.f. chassis a year or so ago, and I was happy with the
radio without it. I wanted to try it in the 390 non-a chassis since the bellows was
already disconnected by the previous owner, or at least loosened easily. I'll
probably forego experimenting with tweaking the bfo injection at this point
(chassis removal fatigue !!) - it's easier to tweak the r.f. gain on real strong ssb

I finished making the shaft coupler out of 6061 aluminum and it works very
nicely. I made it 1/4 inch thick instead of 0.2 inch thick like the original because
that was the thickness of my aluminum plate. All the bending in this gismo takes
place at the thin section at the bottom of the hole opposite the screw so I just
thinned that to 64 mils compared to 80 mils for the original,
so the bending force and stiffness would be about the same. It should have less
stress at the outer side as a result and may last longer. I would guess that all
IF deck tips                                    page 130

failures of these couplers occur either at the bottom thin section or at the root of
the square corner where the screw head or nut sets. If they failed somewhere
else, I would be very suspicious of the type of material
used. I'm only mildly suspicious so far.

I had a failure of each kind in my two couplers. My replacement has somewhat
longer ears where the screw goes to avoid the notched/thin section near the
screw and the shaft hole. I'll keep my eye out for originals to put in the radio
when it leaves me, not soon. Right now I'm happy to have a beefier version
since I anticipate exhanging the two i.f. chassis occasionally without worrying
about breaking them. thanks for
the comments, Dan
From: "Sam Letzring" <sletz@msn.com>
Date: Fri, 31 Jan 2003 18:54:23 -0700
Subject: [R-390] AGC Problems

I have a nice Stewart Warner 390A with a Collins IF module. I can't seem to get
the AGC voltage I think I should get. WIth 30- 40 uv RF in at 1.5 MHz I get
plenty of IF output and > -10 volts output on the Diode load- but < -1 volt on the
AGC line. What should the AGC voltage be? I have seen values quoted up to -10
volts? Any ideas on what I should check? Have checked tubes and caps in the
area of the AGC amps, detectors etc. Any clues will be greatly appreciated.
Date: Fri, 31 Jan 2003 21:20:30 -0500
From: Jim Brannigan <jbrannig@optonline.net>
Subject: Re: [R-390] AGC Problems

I don't recall the correct AGC voltages, but -1VDC seems low. Did you align the
IF, including the AGC amp?
From: "Jim Miller" <jamesmiller20@worldnet.att.net>
Subject: Re: [R-390] AGC Problems
Date: Fri, 31 Jan 2003 22:17:10 -0500

What kind of meter are you using to measure it? If it's a low impedance volt
meter, it may be loading down the AGC line and giving an false low reading.
Date: Tue, 18 Feb 2003 12:44:57 +0100 (CET)
From: =?iso-8859-1?q?fef?= <ik0ire@yahoo.it>
Subject: [R-390] I.F. alignments & BFO

I.F. alignments I am systematizing the my R-390a, anybody could give me of the
counsels in worth to: (1) I want to replace the valve V207" 6AK5," I desire know
like make gives that the valve v207e mail under the group of tuning. (2) When I
insert the BFO order on ON I listen to only that the modulation becomes Dark
but there is not no variation of note acting on the BFO order/ Pitch You excuse
The trouble, here in ITALY has not found people that could Realign l'R-390a.
IF deck tips                                     page 131

Surely I will ask you other counsels for realign my Receiver, you want to excuse
me, Yours sincerely            Frank
Date: Tue, 18 Feb 2003 07:50:19 -0500
From: Bob Camp <ham@cq.nu>
Subject: Re: [R-390] I.F. alignments & BFO

I am not totally sure what problem you are asking about. The stuff below covers
more than one problem. BFO - Here's what I would check - more or less in

1) Swap out V506, V505 and V504.

2) There is a shaft attached from the pitch knob to the BFO coil. Sometimes this
shaft comes loose. Make sure that the coil moves when the knob moves.

3) If you tune to a strong signal with the bandwidth set to .1 KC the BFO should
zero beat with the pitch set to 0. If it does not then loosen the pitch knob and
move the shaft until the zero beat is at 0.

First Crystal Oscillator - V207 - Here's what I would check:

1) Check the tuning on T207

2) Open up the crystal oven HR202 and unplug the crystal Y201. Clean the leads
of the crystal and the oven. Clean the socket that the crystal oven plugs in to. Put
the crystal back in the crystal oven. Put the oven back together. Put them back in
the radio.

3) Swap out V207 and V202.

4) Check that FC no 7 has *not* been done on your radio. If it has then reverse it.
In other words make sure that R210 is 56K ohms and *not* 220K ohms.

5) Check the tuning on T207.
From: "Jim Shorney" <jshorney@inebraska.com>
Date: Sat, 22 Feb 2003 13:20:28 -0600 (CST)
Subject: Re: [R-390] R-390A ....more AGC

How about this? http://www.littelfuse.com/ASP/Search/Detail.asp?ID=522
Bidirectional or unidirectional silicon avalanche surge surpressors, 1500w.
1.5KE10CA are under a buck in single quantities from Digikey. Longer life and
probably faster than a MOV.
IF deck tips                                     page 132

From: flood@Krohne.com
Date: Tue, 11 Mar 2003 10:23:06 -0500
Subject: [R-390] BFO Question

Wow I get to ask my first question! Please forgive my being a bit rusty on
hollow state technology. I had my training during the fall of hollow state and
the beginning of solid-state and as it would turn out I know enough about each
to be dangerous.

My early 60's vintage Amelco R-390A has bfo trouble. It would generate a signal
but the frequency sounded high (sorry did not measure it) and there was very
little adjustment with the dial. A tube swap did not help and looking at the
drawing and being dangerous as mentioned above, I thought that there was not
much that could be wrong there other than the little, pto I think, bfo can. A new
one just arrived from Fair Radio and thus generates, pun intended, my question.
The shaft on the new bfo can is a bit stiff not easily turned by fingers. There
seems to be a bit of oxidation on the shaft bearing. Is it OK to put a drop of oil
on it without risking damage of some type and if so what is the official BFO lube
approved by the list? I certainly don't want to get blacklisted for using solid-
state lubricant.

Is the old bfo repairable? I can't resist opening up little things like this, especially
if it has a stamp telling me not to do so!
Subject: Re: [R-390] BFO Question
From: flood@Krohne.com
Date: Wed, 12 Mar 2003 09:57:16 -0500

Sorry to you and all, I should have mentioned it but I thought of this as well and
removed the knob and tried the whole range of the control. Two or three times
the bfo came to life but any shaft movement would kill it again. That is why I
purchased the new bfo. Thanks,       John Flood KB1FQG

>Did you loosen the BFO knob on the shaft and try to bring it within range?

There is a physical stop on the front panel that keeps the knob from rotating
more than half way in either direction..... but the bfo inductor is a multiturn job.
I've had this happen on a recently acquired R-390A. The bfo would barely come
within range but I just loosened the knob, pulled it back from the stop, zeroed
the bfo, then reset the knob. good luck, Phil
IF deck tips                                     page 133

Subject: Re: [R-390] BFO Question
From: flood@Krohne.com
Date: Wed, 12 Mar 2003 11:12:01 -0500

Oops hit send to soon, Thanks to all who have made suggestions for checking
out the BFO. Perhaps I was not clear enough in my question. I am going to
replace the bfo and I would like to know is it safe to add some "oil" to the shaft of
my new "unused" Fair Radio bfo. I just opened it and the shaft is a bit tight. It
seems to be from a small amount of oxidation from sitting in the box all these
years. Sorry for the confusion here.
From: "Drew Papanek" <drewmaster813@hotmail.com>
Date: Wed, 12 Mar 2003 13:33:32 -0500
Subject: [R-390] BFO Question

John Flood wrote:            <snipped> My early 60's vintage Amelco R-390A has bfo

The BFO knob has a tab providing a robust end of travel stop for BFO shaft. If
knob is installed too far out on shaft, tab is non functional and it is possible to
turn several revolutions. BFO can provides no real stops; forcing at end of travel
will easily break BFO tuning slug partially or completely. This may be your
trouble. Remove and open that can despite those warnings which simply goad
you on! Make a note of wire connection points. BFO slug/shaft can be rejoined
with great care and sparing use of epoxy.

>A new one just arrived from Fair Radio ...........Is it OK to put a drop of oil ...

Oil won't hurt. A lubricant prized by many list members is Mobil 1 synthetic
motor oil. It does not gum up as some others do. Fair Radio is very good about
customer satisfaction; you might consider returning the unit for another
From: "john page" <n8blb@hotmail.com>
Date: Sun, 16 Mar 2003 16:16:15 -0500
Subject: [R-390] looking for parts (V501 fault)

Yesterday I asked if anyone had an I.F chassis as mine had a bad socket. And
since it was in a really hard place to get to I thought I would try to get a new
unit. Thanks to all who responded with help and offers. I thought I would have
one more crack at it before shelling out lots of green. GOOD news. I did fix it.
Acted like a bad socket in that you could wiggle the tube and it would work. Yes
I did try several other tubes. Today I got to measuring voltages at the socket. It
was V501 the first I.F. amp. No B+ on pin 5 but it did have screen voltage on pin
6.It sure doesnt have far to go from pin 5 to pin 6. Well it turned out to be in a
one inch piece of wire from L505 to V501 pin 5. It was broken inside of the
insulation. I was able to repair the wire and now the unit works great. Well
almost great.Now it wont turn off. The filaments stay on as does the dial lights.
IF deck tips                                     page 134

Looks like the micro switch on the function switch is staying closed. That sure
looks like a pain to get to. Oh well I always wanted an instant on 390. Its always
in standby this way. I remember someone saying that this is not good though.
Learning the 390 the hard way, John
From: flood@Krohne.com
Date: Wed, 19 Mar 2003 11:53:17 -0500
Subject: [R-390] Re: [R-390A] BFO Question

Thanks to all who replied with your bfo comments. A drop of oil on the
"unused" shaft smoothed things out a bit. It still was much tighter turning than
the bad one in the radio or other good units that some people had as could not
be turned by my fingers on the shaft. I believe this is caused by an internal (o-
ring?) seal on the shaft, similar to the one used to seal the bfo(pto) case. After
many years of use this wears down allowing the shaft to turn much easier. It
would seem that, this being the case, the new bfo did not have a problem after
all and turns as it should. Perhaps this experience will benefit others in the future.
My Bristol wrench set came in yesterday, I installed the new bfo last night and all
is well. It turns out that the internal core was broken on the bad one. I am
almost brave enough now to drop the front panel and repair the stuck
microswitch on the function control! BTW Am I allowed to listen to anything
other than AM on this fine old radio without getting flamed?
Date: Sat, 29 Mar 2003 09:29:24 -0500 (EST)
From: "David P. Goncalves" <dpg@coe.neu.edu>
Subject: [R-390] R-390(nonA) IF Cans

After a long wait, I have recieved my first (may not be the last) R-390. The
modules have been handled roughly, and there are quite a few scratches, gouges
and dents. Nothing too bad, just looks ugly. Now for my question: Besides the
dents, I'm noticing that the tops of the IF cans are all 'pushed in', andf that the
can nuts are tightened 'till the sides bulged out. Is this normal, or was it a bad
day in the shop for this radio? Is there any harm in banging out the dents?
From: "John KA1XC" <tetrode@worldnet.att.net>
Subject: Re: [R-390] R-390(nonA) IF Cans
Date: Sat, 29 Mar 2003 15:30:17 -0500

Hi David, yes to both of your questions. It's fairly common to see IF
transformers that have been over tightened somewhere along the line, those
deep draw cans ( a piece of art in themselves) cannot support a lot of force
without starting to buckle along the edge. The tops of the cans in my 390 were
buckled pretty good, but they straightened out easily by tapping out the dents
with a wooden dowel against the workbench. The shields cans are just that, only
shields; the transformer frame itself is secured from the inside of the chassis. If
the mounting hole are seem out of alignment after straightening out the cans
you can use a small round file to enlarge the hole a little.
IF deck tips                                     page 135

Date: Mon, 31 Mar 2003 08:46:40 -0800
From: Dan Merz <djmerz@3-cities.com>
Subject: Re: [R-390] R-390A with R-390 IF deck on E-Bay

Gordon, they aren't directly interchangeable without modification. But the 390
IF deck will physically and mechanically fit and can be electrically modified to
operate. This mostly involves rewiring the filaments from series (390 non-a) to
parallel (390a) and a couple of other changes at the underside of the cable
connector plus making up two cable adapters for BNC to mini-BNC. The result
is a nice sounding radio, Dan.
Subject: RE: [R-390] Frequency Shift With AGC Level
Date: Mon, 21 Apr 2003 10:30:01 -0700
From: "David Wise" <David_Wise@Phoenix.com>

> From: Jim Miller [mailto:jamesmiller20@worldnet.att.net]

> I've noticed that with the BFO on a strong carrier, when I lower and raise
> the RF Gain, there is a slight change in beat note pitch, maybe 100 cycles
> or so. This doesn't happen on my other 390a. Have swapped..... snip....

Since the oscillators are unbuffered and not all of the B+ is regulated, there is a
certain small unavoidable shift. However, there is also possibility of avoidable
shift. Make sure the 0A2 is regulating. One of their wear-out modes is a rise in
breakdown voltage. Combined with high screen current and low line voltage, it
may be dropping out. Note also that the BFO uses unregulatedB+ . If you can
rig up a stable external BFO, it will help isolate the shift.
From: "Dave Faria" <Dave_Faria@hotmail.com>
Date: Thu, 24 Apr 2003 19:25:22 -0700
Subject: [R-390] Looking For Suggestions - Stuck Slug

GE List. I scanned the archives looking for a solution to a stuck slug on a 390A IF
Deck. Only one thread in the archives is where a fellow broke a stuck slug. Of
course it's the last slug to be peaked on my deck. Any suggestions? Heat it up
in the oven? Or maybe try the freezer? I'm open for ideas. Lubricants??
From: "Jim Temple" <jetemp@insightbb.com>
Subject: Re: [R-390] Looking For Suggestions - Stuck Slug
Date: Thu, 24 Apr 2003 21:42:19 -0400

I had the same problem a few months ago. I tried to use a metal allen wrench
and, of course, broke the slug. I ended up ordering another from Fair. I have
seen suggestions to heat the coil, and other suggestions to put a couple of drops
of WD-40. Next time I think I will use heat as the first resort. Hair dryer?
IF deck tips                                     page 136

From: "Scott, Barry (Clyde B)" <cbscott@ingr.com>
Subject: RE: [R-390] Looking For Suggestions - Stuck Slug
Date: Fri, 25 Apr 2003 07:48:13 -0500

I think I would refrain from anything like WD40 as it can degrade the coil form.
Date: Fri, 25 Apr 2003 09:10:13 -0400
From: Jim Brannigan <jbrannig@optonline.net>
Subject: Re: [R-390] Looking For Suggestions - Stuck Slug

If there is wax on the slug, then a hair dryer or soldering iron, applied carefully,
should loosen it. Don't use a heat gun, they get way too hot. From painful
experience, do NOT force the issue. The best bet is to try and find a replacement
coil. The coil form is cardboard and will not take much abuse.
From: "G4GJL" <G4GJL@btopenworld.com>
Subject: Re: [R-390] Looking For Suggestions - Stuck Slug
Date: Fri, 25 Apr 2003 17:21:38 +0100

Heated sealing wax in the end of a small blunt stick. Q-tip, 1/8 inch metal stock;
long screw; & a whittled dowel Worked fine for me on a Blue streak project a
while back.
Date: Fri, 25 Apr 2003 13:24:21 -0400
From: Kim Herron <kherron@voyager.net>
Subject: Re: [R-390] Looking For Suggestions - Stuck Slug

I, too, would keep the lubes out of the coil. I've had success drilling out the core
with small drill bits and a pin vise. This, of course, assumes that you have
another core. The actual ferrite core will break up rather easily and the pieces can
be blown out of the coil and a replacement core installed.
From: "Kenneth G. Gordon" <keng@moscow.com>
Date: Fri, 25 Apr 2003 10:15:58 -0700
Subject: Re: [R-390] Looking For Suggestions - Stuck Slug

I have had excellent luck with saving the scraps of smashed slug, grinding them
up with a mortar and pestle, mixing the resultant powder with epoxy glue, and
putting the mix into a straw of the correct diameter.
From: "Bob Tetrault" <r.tetrault@attbi.com>
Subject: RE: [R-390] Looking For Suggestions - Stuck Slug
Date: Fri, 25 Apr 2003 10:36:46 -0700

That is a heroic story to someone who imagines that these things are as near to
magic as they will ever get, but the iron powder is only that, and the straw and
the epoxy is a logical step. The proof is the tune-up and I'm sure that the coil
IF deck tips                                     page 137

peaks as it should. The YMMV part hinges on anyone's ability to use the
minimum epoxy...
From: "Kenneth G. Gordon" <keng@moscow.com>
Date: Fri, 25 Apr 2003 11:56:03 -0700
Subject: RE: [R-390] Looking For Suggestions - Stuck Slug - a possible solution...

Yes. Making slugs with threads on the outside and hex shaped holes in the center
are a lot more difficult, but can be done. The first time I did this was for an R-
1004 with a smashed slug. In that receiver, the IF cans were tuned by a small,
slotted, piece of threaded brass rod with a flat on the slug end. I just stuck the
rod down into the epoxy/iron mix and let it harden. Then peeled off the straw.
Worked beautifully. And as Bob says, you must use a minimum amount of
Date: Sat, 26 Apr 2003 22:09:02 -0700
Subject: Re: [R-390] Looking For Suggestions - Stuck Slug
From: ronald j deeter <k6fsb@juno.com>

I had good luck using super glue gel and a small stick, glue the stick to the centre
of the slug, wait till hard, then slowly remove the core, I had found replacement
cores in other scrap equipment-- Old tv's and junk radios, of course size and
weight are of importance. if it isn't cracked just stuck- try heat the outside and
cold freeze the core -sometimes it works. Re-lubricants-preferably not, be sure
the core is not cracked, however I have used a real light oil (Kano), then cleaned
with alchol, relube lightly with bees' wax
Date: Fri, 02 May 2003 21:02:26 -0500
Subject: Re: [R-390] R-390 Spectrum Analizer
From: blw <ba.williams@charter.net>

> Please share the details of your Q Multiplier hook-up with us. Thanks.

I hooked it up per Hollow State Newsletter #24. I tapped pin one of V204. It says
that it won't affect anything, but audio is a bit lower with the HD-11. It works
well when I need it. It won't do anything to a strong station, but it works very
well on weaker ones. It pulls them right out. I haven't had to null much yet, but I
have tried to null and 'flop' over to peak like I do on a Datong FL-3 on the RBL-
5/Quantum QX Pro loop setup for LF beacons. It doesn't seem to be as sharp
that way. On the Datong, I can catch a weak beacon in a mess of other ones, put
it in null mode and null out the weak one that I want to ID. Then, I just hit the
peak button and that station pops out louder and much, much better. The HD-11
is no Datong FL-3, but it is simple and works using two sides of a 12AX7. One
side for nulling and one side for peaking. No coupling cap is needed. I think the
voltage range is up to 300 vdc. You can get these things for around $25, and it
well worth the money to peak weak stations. I'm sure the nulling will be more
valuable as I use it more. I have a QF-1, which is almost identical, but it needs
something like 160vdc for power to the 12AX7. The HD-11 is easier to hook up.
IF deck tips                                     page 138

Date: Fri, 16 May 2003 18:47:02 -0700 (PDT)
From: Rodney Bunt <rodney_bunt@yahoo.com>
Subject: Re: [R-390] Digital Radio Mondiale

I received a mixer kit from SAT-Service@t-online.de cost 25 Euros (about the
same for dollars US) yesterday in the mail from Germany. It is VERY small.
About 1/2" square. There are few connections, an "in" and an "out" and a volts 7

- 20 v has its own onboard regulator. The LC version specifications say it can be
tuned + or - 12kHz from 455kHz have not hooked it up yet, so it may go to
500kHz. It is so small it can easily be installed inside anything, but my idea was to
build it inside a small 'die cast' metal box, with IF in IF out and volts in using
BNC plugs etc. In this way I could move it around and try it on a variety of rigs.

An ideal solution would be to get the Crystal controlled version and switch in
crystals for the IF's

455kHz IF = 467kHz crystal (supplied)
500kHz IF = 512kHz crystal (still looking for one)
100kHz IF = 112kHz crystal (hopeing to find one....)

 50kHz IF = 62kHz probly easier to make an LC or other higher oscillator with a
divider circuit, a bit on the complicated side so not considering this seriously, but
would be nice to see how the Hammarlund HQ-180 performs or even the
Hallicrafters SX-100. For a R-388, I would connect to the IF out J104 to the "mixer"
then the 12kHz IF out to the sound card input on the PC/laptop and then use the
sound/speaker output to listen to the recovered audio. This needs the 512kHz
oscillator/crystal. No mods to the rig at all. What do you think ????
From: Llgpt1@aol.com
Date: Tue, 10 Jun 2003 21:46:41 EDT
Subject: Re: [R-390] R-390A Cost Reduction and Improvements (was dead horse

> >Has anyone ever tried to brew up a coil/capacitor
> >replacement for the mechanical filters?

Well, we could use the Kiwa filters which have better shape factors and the prices
are not bad. They have better audio qualities and are compatible with any
receiver with a 455 kc if. At present, I use a Kiwa Map Unit with 6 cascaded
filters resulting in bandwidths of 2.9 and 6.8 with shape factors of 1.32 and 1.62
respectively. I realize that many of us won't want to change the filters and want
to continue to use mechanical filters. Then, use the Rockwell/Collins torsional
mechanical filters, beware though, they are expensive. Ya pays yer money and
ya takes yer choices....................
IF deck tips                                     page 139

Date: Wed, 11 Jun 2003 12:46:05 -0400
From: tbigelow@pop.state.vt.us (Todd Bigelow - PS)
Subject: Re: [R-390] R-390A Cost Reduction and Improvements

I seem to recall our pal Nolan posting something about this. Maybe it was Dr.
Jerry, or a combination of both? It all came from the understanding that,
eventually, all of the filters would fail and we'd need to figure out some way to
repair/replace/retrofit them. Might be something in the archives?
Date: Wed, 11 Jun 2003 12:37:15 -0700 (PDT)
From: Joe Foley <redmenaced@yahoo.com>
Subject: Re: [R-390] R-390A Cost Reduction and Improvements

Ok, so what's the recipe, ala R-390 style, for an LC filter?
Can the R-390 filters be used in an R-390A? Or do we have to start from scratch,
winding a coil shouldn't be too tough, selecting a cap to go with it should be
easier. Or do we have to have a tuneable cap for adjustment? Would a slug
tuned coil be better? Any ideas/possibilities for producing a short run of such a
Date: Wed, 11 Jun 2003 16:05:09 -0400
From: Roy Morgan <roy.morgan@nist.gov>
Subject: Re: [R-390] R-390A Cost Reduction and Improvements

>Ok, so what's the recipe, ala R-390 style, for an LC filter?

Would be coil winders, Just look at the design and construction of the R-390 non-
A IF section. Start there. Thrree or four stages of very carefully designed, built,
and tuned "double tuned inductively coupled" IF amplifiers. See Radiotron
Designers Handbook, 4th Edition to get a start on the theory and practice. Then
see Valley and Wallman's RadLab book: Vacuum Tube Amplifiers for stagger
tune methods, if you wish.
Date: Wed, 11 Jun 2003 16:09:40 -0400
From: Gord Hayward <ghayward@uoguelph.ca>
Subject: Re: [R-390] R-390A Cost Reduction and Improvements

Doing the coils shouldn't be too hard. I rebuilt the AGC coil in my R390A using
a slug tuned unit that I found in my box of coils. The trick was to use a big L and
small C to get the Q that I needed. It took me two tries to get it right. The first
try gave a peak, but the Q was so low that it didn't give enough gain to get a
high enough AGC voltage. The second try was dead on and the result meets the
specifications for the performance and the carrier meter calibration is good. I
think the IF strip construction will be a pain. To this end I've thought about
trying (I know this is unrealistic :-) to get an R390 IF deck and adapting it to the
R390A . How about an outboard R392 IF strip? Solid state tubes are another can
of worms that I've thought about. Easier in an R-392!
IF deck tips                                     page 140

From: "Cecil Acuff" <chacuff@cableone.net>
Subject: Re: [R-390] R-390A Cost Reduction and Improvements
Date: Wed, 11 Jun 2003 16:30:36 -0500

Adapting an R-390\URR IF deck to an R-390A\URR is not at all unrealistic.
Seems I remember the Military had it done because of the phase shift problems
the mechanical filters created in diversity operations. There is a military
designation for it...I just can't remember it at the moment. Someone on this list
did the conversion just in the last few months....I remember the posts.... Les
Locklear...Chime in here anytime I know you have the info on it! Finding a
source for R-390\URR IF decks is the biggest problem! (maybe that's what you
meant by unrealistic)
Date: Wed, 11 Jun 2003 14:40:54 -0700 (PDT)
From: "Tom M." <courir26@yahoo.com>
Subject: [R-390] R-390 IF, was Dead Horse, Hi, and Other Subjects.

I've done the 390 IF conversion for the 390A, and so has Gene (I think it was
Gene). Works like a champ. I run it in my regular rig.
Date: Wed, 11 Jun 2003 16:48:33 -0500
From: "Robert M. Bratcher Jr." <bratcher@pdq.net>
Subject: Re: [R-390] R-390A Cost Reduction and Improvements

>Adapting an R-390\URR IF deck to an R-390A\URR is not at all unrealistic.

It's known as the R-275. I saw one at a hamfest 4 years ago in Irving TX.
Should have bought it but I didn't think about it at the time...
Date: Wed, 11 Jun 2003 15:05:57 -0700 (PDT)
From: Joe Foley <redmenaced@yahoo.com>
Subject: Re: [R-390] R-390 IF, was Dead Horse, Hi, and Other Subjects.

Sure, we've covered that scenario. But that burns up already rare R-390 IF decks.
I'm talking about making NEW filters for the R-390A out of discrete, generic
parts, or even custom made parts.
From: "Cecil Acuff" <chacuff@cableone.net>
Subject: Re: [R-390] R-390 IF, was Dead Horse, Hi, and Other Subjects.
Date: Wed, 11 Jun 2003 17:16:19 -0500

I think the KIWA filter modules would be the way to go...unless you are just
trying to go back to L\C filtering...
IF deck tips                                     page 141

Date: Wed, 11 Jun 2003 15:26:46 -0700 (PDT)
Subject: Re: [R-390] R-390 IF, was Dead Horse, Hi, and Other Subjects.
From: <djmerz@3-cities.com>

>Tom/Cecil, I did the conversion and also use the 390 non-A IF. deck all the
time in the 390a - kept the regular 390a i.f. deck in reserve but doubt it'll go back
in. Yes, my biggest problem was finding the 390 i.f. deck which took about a
year of looking and I finally bought one on eBay. I think I've only seen 3 on
eBay since I started looking, and no luck trying to get one out of other guys. At
one point Fair Radio told me they had some parts decks but the price seemed
too high, about $125, if I remember right, to go that route without knowing
where I'd find other parts I might need. I didn't pursue that avenue and ended
up paying about a $100 for the one I have. I doubt that I hear more with the
conversion but it's pleasant listening. Dan
Date: Wed, 11 Jun 2003 18:38:36 -0400
From: Barry Hauser <barry@hausernet.com>
Subject: Re: [R-390] R-390 IF

How about this crazy idea: Leave the original IF deck in there and tap off ahead
of the MF's with a switch or RF plug 'n socket setup to feed the signal into
another rx with a good L/C 455 IF? The other receiver would also need a similar
gimmick. Maybe a crossover switch setup? Actually, the other receiver could be
... brace yourselves .. a NON-A. Or maybe even an SP-600.
Date: Wed, 11 Jun 2003 16:18:22 -0700 (PDT)
From: Joe Foley <redmenaced@yahoo.com>
Subject: Re: [R-390] R-390A Mechanical Filter replacement

Well, yeah, kind of, The KIWA is expensive, I think it would be good if it fit in the
same place as the mechanical filters, too. And, of course, it HAS to sound
good,..... maybe better.
From: "Scott Seickel" <polaraligned@earthlink.net>
Subject: Re: [R-390] R-390 IF, was Dead Horse, Hi, and Other Subjects.
Date: Wed, 11 Jun 2003 19:48:25 -0400

The chemo may have me a bit brain dead these days but it sounds to me like you
guys need to trash the chepo 390a's and get yourselves a quality 390 that needs
no mechanical filter replacements. ( and is more sensitive too)
IF deck tips                                     page 142

From: Llgpt1@aol.com
Date: Wed, 11 Jun 2003 19:17:03 EDT
Subject: Re: [R-390] R-390A Cost Reduction and Improvements (was dead horse

It was the R-725/URR. which used the R-390A and a modified version of the R-
390/URR IF deck. The mechanical filters caused a phase shift in the DF
equipment which was small at the antenna, but when extrapolating it out to the
source, it could have amounted to hundreds of miles in error. Servo Corp. of
America manufactured the IF decks (interesting fact that they were located in the
Richmond Hill area of Long Island) this area was also the home of several other
defense related industries, such as American Trans Coil. My good friend Tom
Marcotte N5OFF documented this in Electric Radio several years ago. Les
Locklear, Gulfport, Ms.
From: Llgpt1@aol.com
Date: Wed, 11 Jun 2003 19:19:14 EDT
Subject: Re: [R-390] R-390 IF, was Dead Horse, Hi, and Other Subjects.

You weren't listening were you, too busy kicking over beehives. Kiwa Industries
has 455 kc filters that have wonderful audio and work great. Better shape factors
than mechanical filters too. Remember this: Mechanical filters will only resonate
so many times and then they die...................end of story.
From: Llgpt1@aol.com
Date: Wed, 11 Jun 2003 19:20:08 EDT
Subject: Re: [R-390] R-390A Cost Reduction and Improvements (

Close, but dyslexic............................R-725/URR
From: Llgpt1@aol.com
Date: Wed, 11 Jun 2003 19:24:14 EDT
Subject: Re: [R-390] R-390 IF, was Dead Horse, Hi, and Other Subjects.

> Leave the original IF deck in there and tap off ahead of the MF's ..........

Kinda like a Hammarlund HC-10 or SPC-10............or, Taaaa Daaaaa a Kiwa Map
Unit. It connects to the 455 if output.Makes it into a whole new receiver.
Date: Wed, 11 Jun 2003 17:40:09 -0700 (PDT)
From: John Kolb <jlkolb@cts.com>
Subject: Re: [R-390] R-390A Cost Reduction and Improvements

The mechanical filter could be replaced with a single IF transformer or one or
two tuned LC circuits, but the overall bandwidth of that filter position will no
longer be 2, 4, 8 or 16 kHz with steep skirts.

Instead, it will be the overall selectivity of the replacement LC tuned circuits plus
the added rejection of the remaining IF transformers in the set. It would take a
IF deck tips                                    page 143

number of hi-Q tuned circuits to match the response of a 2 kHz mechanical filter.
There may be a shortage of R-390A mechanical filters in the Collins "N" case, but
there's not a shortage of 455 kHz mechanical filters - many flow past on that
auction place.

Many could be adapted for use in the R-390A if one doesn't need the
replacement to fit within an "N" filter case. Alternatively, a good ceramic filter
and matching circuitry would fit inside a replacement filter case, and would give
a rounded top response rather than the rectangular top of a mechanical filter, but
could give a good shape factor. (Wouldn't have the MF ringing either)

You can find a couple of R-390A filter plots as well as some ceramic filter plots on
my website, <http://members.cts.com/king/j/jlkolb>
Date: Wed, 11 Jun 2003 22:54:08 -0700
From: "W. Li" <wli@u.washington.edu>
Subject: [R-390] Re: R-390 IF

I like the idea of leaving the original IF deck in, tapping off before the mechanical
filters. How about running the R-390A's 455kc IF signal thru an outboard BC-453
(remember those ARC-5's that we all cut our teeth on?) that has its own 85kc IF
and passable audio. I did this as an experiment and it sounds fine. BC-453's can
be had for $25 or less at hamfests.
From: "Merle" <lal@cyberwc.net>
Date: Thu, 12 Jun 2003 08:47:20 -0400
Subject: [R-390] Meter needed !

Hello to the list.. Just finished rebuilding my first R-392 receiver, works like a
champ ! The meter that came with the radio has a white background with several
vertical green stripes. I have seen pictures of this meter someplace but can't
remember what it was used on. The meter operates but looks strange. I would
like to replace it with the correct meter for the radio. If anyone has one they
might sell or can direct me to a place that sells them I sure would appreciate it..
Date: Thu, 12 Jun 2003 11:29:36 -0400
From: Roy Morgan <roy.morgan@nist.gov>
Subject: RE: [R-390] R-390A Mechanical Filter replacement

>The early mech filters were much more peaky in the passband than what was
>later considered good in the late 75A's and 75S's. As much as 6dB!

Bob, Do you mean either or both of the following..???

1) Pass band ripple in the R-390A filters can be as much as 6 db.
2) Pass band ripple in the filters used in the 75A and 75S receivers is much less
than 6db.
IF deck tips                                     page 144

Date: Thu, 12 Jun 2003 19:15:29 -0700 (PDT)
From: <jlap1939@yahoo.com>
Subject: [R-390] LC sections for the 390a

Joe is legit. I have heard of such a thing, and was told it could be done by an eng,
but I never saw a 390A w/LC filters. Please, if anyone has tried it or knows of it,
reply to us...!
From: "Forrest Myers" <femyers@attglobal.net>
Date: Thu, 26 Jun 2003 20:02:28 -0400
Subject: [R-390] Shaft Clamps

 While putting the IF deck back into my R-390A, I noticed that the bandwidth
switch shaft could not be tightened enough to not slip. Found that the little shaft
clamp was broken. Switched to broken clamp to the BFO shaft and put the BFO
clamp on the bandwidth shaft. They both work now. The BFO shaft is much
easier to turn so the broken clamp is working on it. However, I'd like to get a
replacement clamp to replace the broken one. Does anyone have an idea where
one could be found? Replaced the two blocking capacitors in the IF deck, re-
assembled the rig and fired it up. It still works so it survived the road trip from
Little Rock, AR to Jackson, TN OK. I'm going to have to beef up my work area
before getting serious about finishing up work on the rig. My solid state
workbench is still shaky and too small.
From: "Mark Richards" <mark.richards@massmicro.com>
Subject: RE: [R-390] Shaft Clamps
Date: Thu, 26 Jun 2003 20:49:08 -0400

Forrest, A very fine fellow, Dave Medley, sold a few of these to me a while ago.
He can be reached through: http://www.davemed.com/
From: ToddRoberts2001@aol.com
Date: Thu, 26 Jun 2003 21:45:01 EDT
Subject: Re: [R-390] Shaft Clamps

One source for gear clamps that I have not heard mentioned recently is STOCK
DRIVE PRODUCTS/STERLING INSTRUMENT. They have a catalog that has to
be seen to be believed. You can look through their parts listings online but I
would really recommend you request one of their catalogs.

The one you want is called INCH DRIVE COMPONENTS. They have dozens of
gear clamps in different styles, some identical to the ones used in the R-390A and
they will accept small orders. Also they will manufacture parts to your
specifications. I had often thought about having them make up a number of the
Oldham Coupler assemblies. They can make up an exact copy of the part you
want but not sure how costly it would be. To see them online go to this address :
<A HREF="www.sdp-si.com">www.sdp-si.com</A>. 73 Yours Truly,
IF deck tips                                     page 145

Date: Sat, 05 Jul 2003 10:57:37 -0400
From: Barry Hauser <barry@hausernet.com>
Subject: Re: [R-390] New 390A owner & fan

<snip> Haven't had the chance yet to look deep inside to see what's been
>replaced but it was demonstrated working before I bought it so functionally I
>know that it's basically OK. Functionally, everything seems to work.

Even so, pull the IF deck and look "under the bonnet". Hopefully you have a
spline wrench to unfasten the two clamps on the controls. You should check
C553 (I think) -- that's the mechanical filter killer, should it short out. We
routinely replace those with a new orange drop or other new manufacture cap
as a preventative.

There are clear photos on Chuck Ripple's web site
http://www.r390a.com/ProbCaps.html Also be sure to visit Al Tirevold's web
site http://www.r-390a.net/faq-refs.htm
From: "James Bischof" <jbischof@nycap.rr.com>
Date: Sat, 12 Jul 2003 00:48:55 -0400
Subject: [R-390] agc problem +

AGC problem fixed. It was R546 in the IF deck. Now I have to figure out why I
loose all audio when I turn on the limiter. I am feeling good this morning. I want
to thank every one who responded.
From: ToddRoberts2001@aol.com
Date: Wed, 23 Jul 2003 03:37:59 EDT
Subject: [R-390] Synchronous AM Detector Kit

In case anyone is interested, Steve Johnston WD8DAS is again offering his AM
Sync Detector kit for $159 or assembled for $229. His prices include shipping. His
sync detector uses the famous Sony AM Stereo IC - the same one used in the
Sherwood unit I believe.

The IF center freq is 455 KHz but is adjustable for IF's of 400-500 KHz so it could
be used with other receivers like the R-388/51J-4 with 500 KHz IF. Should work
great with the R-390A. The audio output is around 100mv suitable for connecting
to an external audio amp. I am ordering one and will be glad to report to the list
how it works. You can read more about it at this address :
From: "John KA1XC" <tetrode@comcast.net>
Subject: Re: [R-390] Synchronous AM Detector Kit
Date: Wed, 23 Jul 2003 11:42:02 -0400

fixed mangled link....... www.qsl.net/wd8das/syncinfo.txt
IF deck tips                                     page 146

Subject: RE: [R-390] Synchronous AM Detector Kit
Date: Wed, 23 Jul 2003 11:08:47 -0700
From: "David Wise" <David_Wise@Phoenix.com>

Nope - the Sherwood SE-3 uses an NE602, an NE604, and a discrete VCO.
Date: Wed, 23 Jul 2003 12:37:55 -0700 (PDT)
From: "Tom M." <courir26@yahoo.com>
Subject: Re: [R-390] Synchronous AM Detector Kit

You can also use a Sony 7600G instead of buying the assembled box.
Take the IF from the 390A, tune 455 on the Sony. Voila.
Or take the IF from your 51J, tune 500 and likewise.
Works like a champ.
Subject: RE: [R-390] Synchronous AM Detector Kit
Date: Wed, 23 Jul 2003 12:56:22 -0700
From: "David Wise" <David_Wise@Phoenix.com>

Or an ICF 2010. Sometimes you can get one with a blown front-end for cheap.
It may be deaf for normal use, but it can still hear the IF output.
From: "Scott, Barry (Clyde B)" <cbscott@ingr.com>
Date: Tue, 29 Jul 2003 12:16:01 -0500
Subject: [R-390] S-Meter?

Phil's SINPO ratings prompted me to look up the definition of this code. I
guessed some of it but was unsure of the rest. I found the following link useful.


Curious, though. I paid less than US $600 for each of my R390As. If I had paid
more, would the meters in them be true S-Meters and not just "tuning
Date: Wed, 30 Jul 2003 09:27:55 -0400
From: Gord Hayward <ghayward@uoguelph.ca>
Subject: [R-390] Re: R390A S-meters

I ran a calibration of mine in the middle of the frequency range I use and the
meter was pretty well bang on. Each division was close to the specified 10 dB
and the line was straight. From this I'll claim its a real S-meter. Further, I took
the AGC from the back and scaled it for another Collins S meter (I got it at a
fleamarket so the donor was not killed by my hand!) so it gives real S-units with
S9 beng 50uV at the ant terminal. The delayed AGC means that it won't read
below S6. I use both the meter reading and SINPO in my log and on my QSL
card, just to keep other hams confused!
IF deck tips                                     page 147

Date: Tue, 02 Sep 2003 12:52:24 -0400
From: Roy Morgan <roy.morgan@nist.gov>
Subject: Re: [R-390] R-390A Audio hiss

Adjust the IF gain setting..It is very common for folks who don't understand to
set the IF GAIN adjustment too high. They think it "makes the receiver hotter."
It is a mistake. (It is also a mistake to put higher gain tubes in place of the normal
ones..Check that you have the correct tubes installed, especially the 6DC6 in the
first RF amplifier.) Here is the IF Gain set procedure:


Here is Chuck's procedure:
From: http://www.R390A.com/html/gain.html>
Text in brackets [ ... ] is mine (Roy, K1LKY)
Procedure to set R390A IF Gain:

Once the receiver has been fully mechanically and electrically aligned, the final
procedure to perform before "buttoning it up" is to set the IF gain control. [This
means that you should have done the mechanical alignment - set the cams
properly and so on.] Many otherwise very sensitive R390A's are thought not to
be due to weak signals being covered by noise generated by excess IF deck gain.

 Allow the receiver to warm up for at least 1 hour then:

  1- Terminate the antenna input
         [This means unhook any antenna and put a 50 ohm resistor,or a 125 ohm
         resistor, on the balanced antenna input, no signals from any antenna or
         signal generator.]
  2- Set receiver for 15.2 mHz
  3- Set the "FUNCTION" control to MGC
 4- Select the 4kc filter with the "BANDWIDTH"
  5- Set "RF GAIN" control to 10 or maximum [If your receiver goes whacko
         at this point, reduce the IF gain setting as in step 9 till it behaves right.]
 6- Peak the "ANTENNA TRIM" for maximum noise as indicated on the "LINE
         LEVEL" meter [If you do not get a noticeable peak, your receivers front
         end and rf amplifier stages are not working right.]
 7- Set "Line Meter" switch to -10db scale [minus 10 db]
 8- Set "Line Gain" control to full CW or "10."
         [Local Audio gain 0 or low if you are listening to it.]
 9- Adjust IF gain control, R-519 to cause "Line Level" meter to indicate
         between -4 to -7 VU.
  10- Re-zero the carrier meter control, R-523
         [This can be a touchy adjustment.]
  11- Set controls above for normal operation and reconnect antenna.
IF deck tips                                     page 148

From: "James A. (Andy) Moorer" <jamminpower@earthlink.net>
Subject: Re: [R-390] INFO Cristal Y201 and Y203
Date: Tue, 2 Sep 2003 14:13:18 -0700

(1) Y201, 17 MHz - this will be a SERIES mode crystal

(2) Y203, 200 kHz - this should be a PARALLEL mode crystal with parallel
capacitance of about 30 pF. That will put the proper frequency right in the middle
of the tuning range of the adjustment capacitor. I think the package should be
the HC-6/U package, but I haven't actually looked to make sure. Anybody else
know for sure?

The resistance at resonance will not be critical. Just ask for "as low as is
reasonable". For the 17 mHz, it will be around 400 ohms. For the 200 kHz, it will
be much higher. These can be ordered from JAN crystals. Their inside sales
person is Sue Brick sueb@jancrystals.com I like them because they will make
crystals one at a time. You can order them from the web site at
www.jancrystals.com. Any questions you don't understand on their form, just
don't bother to fill them in. They will contact you if there is a problem.
From: "Dave and Sharon Maples" <dsmaples@comcast.net>
Subject: RE: [R-390] R-390A Audio hiss
Date: Tue, 2 Sep 2003 21:13:42 -0400

All: For those who are also LMR types, I wonder if using a SINAD meter and a
signal generator that does AM would allow us to do this just as well? Seems to
me (but I could be wrong) that checking SINAD at reference sensitivity would
allow the IF gain to be set quite accurately. What does anyone else think?
From: "Richard " <theprof@texoma.net>
Subject: [R-390] INFO Crystal Y201 and Y203
Date: Wed, 3 Sep 2003 20:35:29 -0500

I purchased the crystal oven with both crystals from American Trans-Coil
http://www.atc-us.com/ for US$13.00. This may be a cost effective source even
if you do not need the oven.
Date: Sat, 27 Sep 2003 20:51:17 -0700
From: Chuck <ka6uup@pacbell.net>
Subject: [R-390] R390A Popping

My R390A has recently developed a problem. During ordinary listening
conditions in either AM or SSB, it pops at regular intervals. The signal strength
meter jumps when this occurs. But, the pops are not always the same amplitude
on the meter. The popping seems to respond to a change in agc settings. At first I
thought it was external interference as it quits when the antenna was
disconnected. However, after comparing other receivers in the shack and
IF deck tips                                     page 149

hearing nothing, I came to the conclusion it is internal. Before tearing into the
radio I thought I would ask the group for ideas and suggestions
From: "Russell Barber" <rfidman@pacbell.net>
Subject: Re: [R-390] R390A Popping
Date: Sat, 27 Sep 2003 21:28:44 -0700

I also have a R-390A and am hearing a popping sound. In my case however I am
hearing it on my R8500 as well. I had to use the wide Am bandwidth setting and
turn the noise blanker off. I never heard this popping until I moved out to
California. I have heard this popping at a different QTH in town so I know it is
not local to my house. The limiter on the R-390A does eliminate the popping
but at the expence of some fidelity.
Date: Sat, 27 Sep 2003 21:22:38 -0700 (PDT)
From: Joe Foley <redmenaced@yahoo.com>
Subject: Re: [R-390] R390A Popping

That sounds like an electric cattle/horse fence in the area.
From: "Dave Faria" <Dave_Faria@hotmail.com>
Subject: [R-390] R390A Popping
Date: Sun, 28 Sep 2003 08:04:56 -0700

GM Chuck. I have had a similar problem but, its been a few years and I don't
remember if the "pop" occurred at regular intervals. If u have use of an o-scope
and tube extenders look at the trace around the tubes and see if that gives u any
clues. What I have had on two 390 non "a" radios is a failure of the coil just after
the final mixer. I think its t-207 on the 390 non "a" and it might be t-208 on the
390a. One of my coils was in the process of failing open and was causing the
same popping sound. The 390 manuals give a dc resistance for the winding of
each coil so pop the coil cover and check. Incidentally for those who are
interested I sub'ed a 390a mixer coil into the 390 non"a" and it works fine to this
From: jamesmiller20@att.net
Subject: Re: [R-390] R390A Popping
Date: Sun, 28 Sep 2003 05:04:37 +0000

I had the same problem. Unfortunately it turned out to be a break down in the
center insulation of the mini-coax cables carrying the diode load signal from the
IF module, to the rear terminal strips, up to the front panel, etc. After tediously
replacing these coaxes the problem went away. I was put onto this by another
on the list several years ago who had experienced the same thing. I forget who.
Popping will tend to be more noticable when the diode load voltages go higher
due to the breakdown in the coaxes. Strange but true. Of course it could be
otherthings too, like bad caps, a bad tube, etc. Good luck.
IF deck tips                                     page 150

Date: 5 Oct 2003 14:21:31 -0000
From: "Walter Wilson" <wewilson@knology.net>
Subject: Re: [R-390] R390A Popping

I may have been the "other" person on the list, as I had this same problem and
have shared it with some. The problem was in the small coax cable that goes
connects the limiter to the diode load. It was very tough to troubleshoot, and
finding it was mostly a process of elimination. I was able to unsolder the coax at
both ends, and test with a piece of coax jumper prior to removing the old coax
and relacing it back into the wiring harness.
From: "JamesMiller" <jmiller1706@cfl.rr.com>
Subject: Re: [R-390] Capacitor Heresy
Date: Sat, 1 Nov 2003 13:48:09 -0500

<snip> Another thing I discovered in this radio... on one band (the upper AM
broadcast band) the carrier meter would change about 10-20 dB for no apparent
reason, usually a function of how long the radio had been on. It would play solid
60 dB on the local station for 30-45 minutes, then suddenly drop 10-20 dB. It was
a local station and this was not due to propagation changes. After much head
scratching and deduction, this was finally traced to an intermittent failure in a
capacitor in one of the band coils. It was in coil Z202-1, a 2400 pf cap (C-235-
1)inside the coil can ... one end of this cap "touches" the B+ line feeding the V201
RF Amp via the coil in Z202. The other end of this cap. is in series with a 180 pf
cap, both across the coil. My suspicion is that the radio was used a lot by the
previous owner on the broadcast band, hence this cap. was subjected to B+
longer than any others, and developed a failure. Alternately, the higher value
combined with aging resulted in a voltage breakdown of some kind. The failure
didn't change the resonance of the coil greatly, but enough to reduce the signal
coupled to the next stage. I bought a new can and it works well now. I suspect
that any questionable performance on other specific bands could be traced to
similarly failed capacitors in the coil cans for those bands (C232-1, C234-1, C238-
1, etc). The moral is don't forget internal failures in these cans when diagnosing
problems. (PS I got the replacement can from Fair Radio)... <snip>
Date: Sun, 09 Nov 2003 19:24:03 -0600
From: flderoos@mmmpcc.org
Subject: [R-390] A Bunch of Questons About an R390A

I've been working on a R390A that I got through a trade and have several
questions. It is basically a Stewart Warner receiver (RF deck and chassis), but the
IF module is an EAC, the audio and power modules are Collins and the PTO is
Cosmos. So far I've recapped it and checked the values of most of the resistors.
I've replaced the power cord with a 3-wire cord and cleaned and the gears,
bearings and slides. As soon as the Deoxit arrives and I can clean switch contacts
and assorted sockets, I'll put it together and see if it works, then align it. Now to
the questions.
IF deck tips                                   page 151

I decided to measure the resistance from the AGC lines to ground. The IF
module showed infinity, as it should. I then measured the AGC line on the RF
deck and found approximately 80 K ohms (way too low). I don't know why I
did this, but while troubleshooting I removed V203 and V204 and found that the
resistance went up to 3-4 megs (better). Well that suggested some pretty bad
tubes if they could show low resistance from grid to ground without the
filaments on. After checking them and finding them to be ok (no shorts and not
gassy) and subbing them with known good tubes and finding the same decrease
in resistance, I started looking at how they were wired. The first thing I noticed
is that the 27 ohm resistors that go to the grids were connected to pin 1 on each
tube. A quick check of the base drawing shows that pins 1 and 5 are internally
connected, so that explained why with the tubes inserted I got the low resistance.
I was measuring the resistance of the B+ line to ground! Well, with further
checking, I found that the cathode resistor/capacitor was connected to pin 2 of
V203 and to pin 7 of V204 and there was a jumper to pin 2 on V204. So, it
appears that the jumper was left off of V203. Now the real strange observation,
pin 6 (grid) of V203 and V204 were both connected to ground!!! I've never heard
of a grounded grid convertor. So, the first question is does this mod look at all
familiar to anyone? Was there a mod that just didn't get completed correctly or
was there a tube change?

Now the second question. The AGC line to V201 goes through R201, which is
listed as a 270k resistor. My deck has a 3.3 meg in parallel with a diode for R201
with the cathode toward the transformers. It also has R233 replaced with a 3.3
meg resistor and another 3.3 meg resistor from E208 to ground. I seem to
remember a change in the AGC for the RF amp, but can't remember it. And the
third question is what is the purpose (if there is one) of an added diode between
terminals 3 and 5 on TB102? This is the AGC DIV/NOR connection on the back.
I forget the number, but it is a 3-digit number and looks like it might be a
germanium diode.

And the final question is what should the DC resistance of the mechanical filters
be? Three of mine measure 50 ohms for the input and output and the other one
(8 khz) measures 40 ohms for the input and the output. I think I've seem 40
ohms listed several times, but am surprised that I would have three bad filters
that measure so closely. And, if there were shorted turns, the resistance should
be lower. These are quite the receivers. I can't wait to get it working and actually
use it. Thanks in advance for any help/suggestions.
From: "JamesMiller" <jmiller1706@cfl.rr.com>
Date: Wed, 19 Nov 2003 22:14:06 -0500
Subject: [R-390] Clavier IF Module - Ugh !

Wow! Working on a EAC 390a that has a Clavier IF module, ... unbelievable.
Couldn't get the IF module to behave, occasionally it would slowly loose gain
then it would come back again. Plus some strange intermittants. I discovered
that one of the IF amplifier tubes would loose filament (making the gain go
away slowly) then it would come back. Found that the ground lead to the
filament pin had not even been soldered at the factory! Wire was looped
IF deck tips                                     page 152

through the socket pin, but not soldered! That explained the intermittent
filament. Soldered it and that particular problem went away, but now another
intermittent around another tube. Again, another pin not soldered, and three
loose screws holding ground lugs. While I was in it, I did a complete check of all
joints, and found 3 more suspect/cold solder joints as well. Well finally, the IF
module works fine now, but Clavier must have had miserable quality control!
Didn't they also make electric organs?
Date: Thu, 20 Nov 2003 05:04:32 -0800 (PST)
From: "Tom M." <courir26@yahoo.com>
Subject: Re: [R-390] Clavier IF Module - Ugh !

All modules were supposed to be inspected by a govt inspector so sounds like
the system broke down. I suspect your module was an over run and never made
it to service. What is the contract/s.n.???
From: "JamesMiller" <jmiller1706@cfl.rr.com>
Subject: Re: [R-390] Clavier IF Module - Ugh !
Date: Thu, 20 Nov 2003 17:40:39 -0500

The order # on the Clavier IF is DAAB05-70-C-1194; SMC 343621; SN 15

Wow! Could this be a collectible? I bought this radio a couple years ago from a
guy who said it was EAC, just now getting around to rejuvinating it. Everything
else appears to be EAC except for the IF and the Cosmos. IF works fine now so I
guess it doesn't matter except to the purists. I'm refurbishing the radio to the
point where I want to sell it back into the "pool". Replacing the "problem" caps,
linearizing the PTO, etc. I have two others (a Collins and a Stewart-Warner),
which is already one too many. If anyone is interested in this EAC with a Clavier
IF, fixed and working when I finish going thru it, let me know. This is not a
mechanical rebuild as Mish or other experts would do, but it will be working well
electrically when I finish, a good starting point to continue from. The front panel
probably needs a repaint - it's the etched variety. Knobs and dial cover probably
could use a repainting too. I'll probably take a loss selling it, but I need bench
space in the garage.
From: "Joel Richey" <richey2@mindspring.com>
Date: Sat, 22 Nov 2003 10:44:33 -0500
Subject: [R-390] Bracket for cxr adj pot./

Tnx to all who offered one of these, I wasn't able to respond to everybody who
offered, now Iam looking for the 8KC filter for the R390A if anyone has one they
would like to sell I would be interested as long as I don't have to get a 2nd
mortgage on the homestead. Got a question, the cxr meter pegs on strong sigs
and funny thing is it does it with different IF modules, behaves the same with
either of 3 IF modules I have, anybody seen this before.. Tnx
IF deck tips                                     page 153

Date: Sat, 22 Nov 2003 09:19:58 -0800 (PST)
From: John Kolb <jlkolb@cts.com>
Subject: Mechanical Filter --Was [R-390] Bracket for cxr adj pot./

See <http://members.cts.com/king/j/jlkolb> and follow the links
to the For Sale - Mechanical Filters and Crystals page. I've also got plots of the R-
390A filter responses for anyone that might find them of interest.
From: "mparkinson1" <mparkinson1@socal.rr.com>
Date: Sun, 23 Nov 2003 22:06:33 -0800
Subject: [R-390] OSC Deck

Does anyone know it the R-1247 Osc deck is the same on the R-390a deck and if
so are the all the cables the same to do a direct hook up. Someone asked me this
and I have never seen a R-1247 so I could not give them an answer. Surely
someone other might know this question.
Date: Tue, 25 Nov 2003 09:11:31 -0500
From: MURPH <rickmurphy1001@earthlink.net>
Subject: [R-390] R390 IF strip conversion

Does anyone know where I can get information for converting a R390 IF strip
for use in a R390A ? Thanks in advance
From: R390rcvr@aol.com
Date: Tue, 25 Nov 2003 09:27:29 EST
Subject: [R-390] R-390 IF Strip into R-390A

Tom Marcotte did an article in ER , Dec,2000 on the process. Someone probably
has that article, or perhaps you could contact Tom directly. courir26@yahoo.com
Date: Tue, 25 Nov 2003 08:10:48 -0800 (PST)
From: "Tom M." <courir26@yahoo.com>
Subject: [R-390] URL for R-390 IF conversion

I've posted the requested text to this URL:
Hope this helps. I've been running this 390 IF deck in a 390A for a couple of
years with no problems.
Date: Tue, 25 Nov 2003 08:14:37 -0800
From: Dan Merz <djmerz@3-cities.com>
Subject: Re: [R-390] R390 IF strip conversion

Hi, I strongly recommend the ER article by Tom. I successfully did this
conversion and was very pleased with the result. It's stayed installed since I
made the conversion. The toughest part for me, besides finding the 390 IF.
IF deck tips                                    page 154

chassis in the first place and soldering in cramped quarters, was finding the
adapters for BNC to mini MB connectors for the two cables. Since then they are
showing up on eBay all the time, under $20 each - I made mine up using a small
junction box with 2 chassis mount mini connectors from Fair Radio connected
directly to the bnc cable coming thru small holes in the box going to bnc
connectors on the other ends of the cables. The adapter you need is the type that
is chassis mounted on the 390a for the i.f. output at the rear if you don't want to
fuss with building a box like I did. Hope this helps, Dan.
From: "Dallas Lankford" <dallas@bayou.com>
Date: Wed, 24 Dec 2003 15:32:46 -0600
Subject: [R-390] USB & LSB Filters and BFO Fine Tuning

For several years I have had some high impedance USB and LSB filters which
require 130 pF resonating capacitance. These seemed like ideal USB and LSB
filters for the R-390A, except for the work involved in removing the original
filters and installing these, and these did not have flanges. Flanges are essential,
otherwise RF will leak around the filters. Making and fitting the flanges to the
filters turned out to be easier than I thought. Details of this mod can be found in
the FILES section of the YAHOO R390 group. The obvious advantage of this
mod is that you can set the BFO PITCH and forget it.

There are several reasons why an unmodified R-390A is not a great SSB receiver.
Fortunately, most of these have been addressed in the past. The KCS tuning rate
has not, mainly because there seems to be no way to add fine tuning to the KCS
tuning. The BFO tuning rate has also not been addressed generally, though
there were a few R-390A's with BFO reduction tuning gizmos with a counter dial.
I never used one, so I can't say whether it solved the SSB tuning problem or not.
My BFO tuning mod uses voltage variable diodes, and works very well. The
tuning range is 200 Hz (for 1 turn), which is equivalent to a 30:1 reduction in the
BFO PITCH. You tune in a SSB signal as well as you can with the KCS knob, and
then clarify the signal with the BFO fine tuning knob. The knob is attacked to a
pot which is installed in the DIAL LOCK hole. This mod can also be found in the
FILES section of the YAHOO R390 group.
From: "Dallas Lankford" <dallas@bayou.com>
Date: Wed, 24 Dec 2003 21:01:16 -0600
Subject: [R-390] More USB & LSB Filters

I forgot to mention that I don't know where I got the 526 9365 000 and ...65 000
filters. I also have a pair of 526 9364 061 and ...65 061. They seem to be the same
filter, except perhaps for a bit wider bandwidth. That doesn't matter if you use a
6 kHz roofing filter like I do. I believe I got the ...061's from Surplus Sales Of
Nebraska several years ago for $100 each.
IF deck tips                                     page 155

From: "Drew Papanek" <drewmaster813@hotmail.com>
Date: Tue, 27 Jan 2004 18:13:39 -0500
Subject: [R-390] RE: HSR-2 vs 390a

On an Electric Radio article comparing the simple HSR-2 vs the R-390a, Dan Merz

What caught my attention was the statement –

>"Comparison to my very well working 390a was dramatic, I could CLEARLY
>hear signals that were well under the hash level of the 390a, but very
>comfortable copy on the homebrew receiver." (snipped) But what I'm
wondering about, are there other factors that would make the 390a inferior in
>certain cases to a simple receiver as expounded in this article?

The aforementioned statement regarding HASH level of the R-390A could have
some basis even for a well-functioning R-390A. The R-390A's mechanical filter
response has extremely sharp skirts; wonderful in crowded ham band
conditions but not so good in impulse noise situations. Hash as we sometimes
define it is a form of impulse noise. Those filters will ping and ring, "smearing"
out the pulses and making interference worse. One listening to a high quality
AM signal with the R-390A can hear a slight raspiness to the audio; the filters ring
on transient modulation peaks. The R-390 non-A has LC filtering (the IF cans)
which has a more gradual skirt characteristic largely devoid of ringing and hence
does far better in the presence of impulse noise. That also accounts for the
superior audio quality of the non-A. I have an el cheapo Hallicrafters S-120 which
is a low entry level general coverage receiver. Tube lineup is the All-American
Five minus the 35W4 (selenium instead). Normally in side by side comparisons
a signal that is not even detectable on the Halli will be armchair copy on my R-
390A. But enter strong 60 Hz power line hash and on moderate strength signals
the great '390A is humbled by the lowly Halli.

Rolling your own R-725 by stuffing the non-A IF module into an R-390A has its
merits. However, that module can be hard to come by.

Here are some ideas (possibly without merit) I've been pondering for R-390A IF
module modification. (Forum Tranquility Preservation Statement: Performing
the following modifications would constitute heresy! Shame upon he who
would attempt them!)

1.Replace one or more of the "mechanism a philharmonic" (mechanical filters)
with a filter comprising cascaded LC sections. These could be modern miniature
IF cans with added impedance matching in and out. Modern ceramic filters plus
impedance matching schemes could also be used.

2.Bypass 16 KHz filter entirely, add attenuation to match losses in the remaining
filters. Change values of or remove the Q spoiler resistors in the R-390A's IF
cans. Realign with less (or even no) frequency staggering. Fiddle with cathode
IF deck tips                                     page 156

resistors to reduce the gain which was raised by can mods. The IF cans so
adjusted would then define bandwidth in the switch position labeled "16 Kc".
That would be the high fidelity, impulse noise resistant mode. Using the
narrower bandwidth positions would then provide mechanical filtration at the
original bandwidths (provided the filter in use had a narrower bandwidth than
newly defined by IF cans). Original function (and susceptibility to impulse noise)
in the narrower positions would be preserved. These modifications might be
attractive to one whose IF module has a defunct 16 KHz filter, if not for the fact
that the 4Khz filter fails most frequently.

3. Keep the Philharmonic Quartet (16, 8, 4 ,2 Khz) intact but add relay switching
to put the Quartet on hold and swap in LC or ceramic filtration as desired.

4. Add that panadaptor output jack you've been thinking about and use it to
feed an external IF/detector/audio unit.

A better "modification" might be to acquire the R-390 non-A.
From: "Cecil Acuff" <chacuff@cableone.net>
Subject: Re: [R-390] RE: HSR-2 vs 390a
Date: Tue, 27 Jan 2004 17:40:15 -0600

Those sound like some good ideas to check out...I had thought about the IF deck
mod to replace the Mechanicals with some LC filtering or ceramics. I know
many new radio's now days can be ordered with the Collins mechanicals or
ceramic filters so there must be some level of interchangeability.
From: "K1KQ" <k1kq@motorhomesusa.com>
Date: Wed, 28 Jan 2004 09:09:10 -0600
Subject: [R-390] OOPS! C-553 not C533

My post should have read C-553 not C-533... Damn that spellpecker.

>> "I have decided to take the conservative approach with respect to C533 and
replace it" <<
Date: Wed, 11 Feb 2004 17:18:16 -0500
From: Jim Brannigan <jbrannig@optonline.net>
Subject: [R-390] Hum

I have a '67 EAC R-390A with a low level hum that is making me crazy. The hum
is controlled by the AF gain control and therefore before it. It is influenced by
the 800cps bandpass filter and disappears when V601 (1st AF amp) is removed.
The plug in Capacitors have been replaced with new electrolytics. C609 in the
cathode circuit has been replaced and the Rippel audio mod installed. The tube
has been swapped for another and the hum still persists. Short of replacing every
component in the 1st AF amp, I'm stumped!! Any suggestions?
IF deck tips                                     page 157

From: "John KA1XC" <tetrode@comcast.net>
Subject: Re: [R-390] Hum
Date: Wed, 11 Feb 2004 21:53:44 -0500

Hi Jim, the hum might not be in the audio deck. Here's some tips..... Does it go
away when you click ON the noise limiter? If so bypass cap C536 in the IF deck
could be open. You could also have filament to cathode leakage in one of the
detector or noise limiter tubes. To further isolate the trouble, disconnect the
Diode Load jumper (TB103 terminals 14&15) which will break the connection
from the detector and see what happens.
Date: Thu, 12 Feb 2004 08:10:52 -0500
From: Gord Hayward <ghayward@uoguelph.ca>
Subject: [R-390] Hum

I had a similar problem and as John mentioned, it was a filament to cathode leak
in the noise limiter. The impedances in that stage are high so the leak was small
enough not to show up on my tube tester, but big enough to give lots of hum.
Replacing the tube fixed the problem, but I only found it by substitution.
From: "AI2Q" <ai2q@adelphia.net>
Subject: RE: [R-390] Hum
Date: Thu, 12 Feb 2004 15:43:22 -0500

Jim: Tighten down all under-chassis hardware, such as terminal strip grounding
points. That cured a nasty 60-cycle audio hum problem here in a recent 51J-4
overhaul on my bench.
From: "Bernie Nicholson" <vk2abn@batemansbay.com>
Date: Fri, 13 Feb 2004 12:24:02 +1100
Subject: [R-390] 390a hum

I had hum in my 390a and after some searching I found that it was caused by
heater cathode leakage in the 6BA6 in the VFO replacing the tube fixed the
problem But I initially looked in the audio and IF module
From: "Steve Hobensack" <stevehobensack@hotmail.com>
Subject: RE: [R-390] agc repair
Date: Mon, 12 Apr 2004 20:03:23 -0400

Gene, AGC voltage is very feeble. Any gassy/leaky tube, usually a 6BA6, or a
leaky cap in the AGC circuit will suck down the voltage. There is no easy way to
find the leaky cap. It usually involves cutting one end free, and using a megger
or the old fashined magic eye cap checker. Good luck.
IF deck tips                                     page 158

Date: Tue, 13 Apr 2004 08:35:03 -0400
From: Gord Hayward <ghayward@uoguelph.ca>
Subject: [R-390] Re: AGC repair

Another thing to check is the antenna trimer. Its shaft is live to AGC. That is
why the isulated bushings are important. Spraying with even a slightly
conductive lubricant is bad news.
Date: Sun, 11 Apr 2004 16:12:06 -0400
From: Bob Camp <pb@cq.nu>
Subject: Re: [R-390] agc repair
To: Gene Dathe <dathegene@hotmail.com>

With "no agc voltage at all" (I assume that means zero volts) I sure would check
the resistance of the AGC line to ground. It sounds like a short in one of the
bypass cap's or cables. Assuming you find a short at the back panel TB102 then
unplug the modules one by one. Either the short will go away when one of the
modules is unplugged or the short is in the main wiring harness. If it's in the
harness check the normal pinch points.                    Hope that helps.                  Bob Camp
Date: Fri, 16 Apr 2004 19:47:00 -0700 (PDT)
From: "Tom M." <courir26@yahoo.com>
Subject: [R-390] Build Your Own R-725 Link

I was asked to furnish the link to this article, so I thought I'd also post the link as
well:      http://www.geocities.com/courir26/r725conv.htm

Spend your summer lining up parts for fall completion. Since I did this project a
few years back, I hope I can still find my R-390A IF deck.
From: "John KA1XC" <tetrode@comcast.net>
Subject: Re: [R-390] agc repair
Date: Sat, 17 Apr 2004 00:54:17 -0400

I've fixed three "no AGC" problems and none involved leaky caps or tubes,
although the former can certainly degrade AGC action. The one that was
toughest to find but easiest to fix was a 390A that acted like the AGC line was
shorted to ground but the resistance measurements looked OK. The problem
was that one side of the diversity OR-ing diode on the rear terminal had been
bent over and was touching the chassis, so it was clamping the AGC line to
within a few tenths of volts to ground! The other two problems each occurred in
a 390 and 390A IF module. The Zxxx coil that is the resonant plate load for the
AGC amplifier tube opened up and thus the poor tube wasn't getting its B+. Had
to replace that coil in each IF. :^( 73, John
IF deck tips                                     page 159

From: "D. ball" <ke1mb@hotmail.com>
Date: Thu, 22 Apr 2004 14:14:17 -0400
Subject: [R-390] To un-mod or not

I have just recently bought a 59’ Steward-Warner. It is in really good condition
but with some mods. My first question is, a co-worker who worked on the 390’s
in the service believes that if a mod was done by military personal under factory
approved updates then that mod should be considered “stock”, and under a
collectors point of view it be valid. I would like to know if the 85’ vintage radios
had tubes instead of diodes. Secondly is someone made some IF mods in my
radio. V506 seems to be a diferential product detector now. And there are
various diodes in the AGC section which I have not mapped out. It all works
very nice. But I don’t use the radio that way. I use the IF out. That way I can play
and not cut up the radio : ) I notice that when I use my Kenwood 930s as the
demodulator (with 60db of pad) I get very good results with the 390 on MGC. I
am wondering if the stock ACG would work better using the 390 as a down
converter only. I don’t plan on selling this radio, the best city radio ever!! With
the kenwood 930 dialed up on 455kc +/- some, and the 390 as the front end, I
hear things neither radio can hear by itself. It is a scary combination.
Date: Thu, 22 Apr 2004 14:06:27 -0400 (EDT)
From: <ah7i@atl.org>
Subject: Re: [R-390] To un-mod or not

> I don’t plan on selling this radio, the best city radio ever!! With the
> kenwood 930 dialed up on 455kc +/- some, and the 390 as the front end, I
> hear things neither radio can hear by itself. It is a scary combination.

You answered your own question...
Date: Thu, 22 Apr 2004 21:57:35 -0400
From: Bob Camp <ham@cq.nu>
Subject: Re: [R-390] To un-mod or not

Odd but true - most receivers do not present a 50 ohm load to the antenna.
When you pop a radio on to the 455 KHz output of the R-390 you put a "strange"
load on the 455 KHz output of the radio. Like everything else on the 390 it will
do better if you align it with that load in place *if* that's the way you are going to
run the radio. A second thing to play with is the good old IF gain adjustment.
You may find that a lower gain setting will still drive the outboard radio and give
you better overload performance. Since both of these adjustments are reversible
there's not much risk in trying them to see if they help or not.
IF deck tips                                     page 160

From: "D. ball" <ke1mb@hotmail.com>
Subject: [R-390] To un-mod or not
Date: Thu, 22 Apr 2004 23:42:41 -0400

The buffer amp in the 390a does a good job, but regardless i have to use 60db of
attenuation between the IF out and the kenwood 930. The signal is too hot
otherwise, here you get a perfect 50 ohm load for the 390's IF out. The 60db is a
must, you will overdrive your HF rig without it.
Date: Fri, 23 Apr 2004 10:13:31 -0400
From: Bob Camp <ham@cq.nu>
Subject: Re: [R-390] To un-mod or not

> The buffer amp in the 390a does a good job, but regardless i have to
> use 60db of attenuation between the IF out and the kenwood 930. The
> signal is too hot otherwise, here you get a perfect 50 ohm load for
> the 390's IF out. The 60db is a must, you will overdrive your HF rig
> without it. D. ball

One option might be to move the IF pick off point closer to the start of the IF
chain. Obviously this involves modification to the radio ... One good option
might be to use a scrap IF strip that's missing a couple of the filters. That would
leave your "real" IF strip intact.
Date: Fri, 23 Apr 2004 13:28:47 -0400
From: wwarren1@nc.rr.com
Subject: Re: [R-390] To un-mod or not

It's even easier than that, simply disconnect the plug bringing the 455 kHz IF
signal from the RF deck to the IF deck and use that signal to go the auxilliary
receiver. Yes, one misses the mechanical filters of the 390A, but one also misses
the intermod of the first IF stage, which according to some of the
documentation, is one of the main sources of troubles. However, with that
setup, you'd be getting the image rejection and selectivity of the 390A front end.
Remember that the IF deck is set up for 150 microvolts input at 455kHz for -7
volts on the diode test point. Thus, the RF deck as the front end to the aux
receiver may still be too hot. That is, approximately a 2-4 microvolt input to the
390A antenna will deliver 150 microvolts to the RF deck, and that's about a
-83dBmw signal. -83dBmw shouldn't overdrive the aux receiver, but with
presumably no AGC on the 390A RF deck, the signal will go up very
considerably (should be linearly) with increased antenna signal strength. Hope
this all makes sense.
IF deck tips                                     page 161

Date: Thu, 03 Jun 2004 10:55:13 -0400
From: Roy Morgan <roy.morgan@nist.gov>
Subject: Re: [R-390] Solid State Ballast 'quirks'?

> ... If I was going to bet on the cause it would be a loose connection........


Bob's comment is right on, but reveals a possible other mis-adjustment. If the IF
strip is contributing much at all to the set's noise (with the RF section not
working), its gain is probably set too high.

See the procedure to set the IF gain on Chuck's website at
http://www.r390a.com/ and specifically at: Under "Technical": "Setting the IF
Gain for Maximum Performance"

Note: "Terminate the antenna input" means put a resistor across the two
balanced input pins of about 100 to 200 ohms. The basic concept of this
adjustment is that the radio's internal noise should come almost entirely from
the first RF stage for best performance.

It's common for folks to crank the IF gain adjust pot up so they get louder
signals. This upsets the carefully designed balance of gain in the various stages of
the radio and leads to reduced performance - particularly in small signal
detection capability and in overload and cross modulation characteristics. Those
who used to service these sets in military situations where small signal
performance was very important report that new RF front end tubes are noisier
than those with some hours on them. So if you are tweaking for best noise, use
a broken-in 6DC6.

> .. It's good to have a VTVM to do the measuring with. ... .........

See this link for a Heath V-7A priced at $15. (I still have the one I
built in about 1959, and it runs just fine!): http://www.af4k.com/miscpart.html
If you want a genuine TS-505 as specified in the R-390 manuals, here is one:

>TS-505 VTVM ("http://www.w2ec.com/ts505.jpg"), includes cover and probe.
>$25 plus shipping from NY 13732 Ray W2EC "w2ec@bmjsports.com"

These VTVM's have a meter face that is a bit harder to read than the Heath, but
they are quite indestructible. By rights, no R-390 repair person should be
without one for authenticity. It has been rumored that very difficult to find faults
in R-390 receivers have cured themselves permanently when the TS-505 was
turned on and brought to bear.Note that this meter also has an AC/RF probe
that is useful from 30 cps to 10 mc and below 40 volts RMS. The diode used is a
1N70 germanium diode, not the hard to find and expensive vacuum tube ones
found in the HP 410 meter probes. If you blow it out, a modern PIN diode will
IF deck tips                                     page 162

likely work just fine. By the way, the same fellow has a URM-25D that has been

>URM-25D Signal Generator "http://www.w2ec.com/urm25d.jpg"), perfect
>operational condition, with manual copy and HSN reprint of Dallas
>Langford notes. All caps have been replaced per the HSN notes.
>Also includes accessories as shown: ("http://www.w2ec.com/urm25dacc.jpg").
>$125 plus shipping from NY 13732
Date: Sat, 12 Jun 2004 17:47:34 -0400
From: "Dee C. Almquist" <w4pnt@velocitus.net>
Subject: [R-390] SPECIAL R390A PANEL (6kc & 8kc)

Have you ever considered a narrower filter like 6kc & move the 8kc filter to the
16kc slot, eliminating 16kc? This means re-silk screening refinished panel that
puts 6kc where 8kc position was & changed 16kc to read 8kc with same fonts as
original. I have some pics of one done this way. Its pretty neet & I think I will
modify my 390A this way when I restore it. That 16kc filter is much too broad &
I seldom use it. But I use the 8kc a lot. And 6kc is just right for AM operation with
reasonable band conditions.

Because of a request for 2 special R390A panels, I have the screen in stock to do
many more this way. Cost Will be $135. for this "special", front side.
Date: Sat, 12 Jun 2004 21:38:53 -0500
From: Tom Norris <r390a@bellsouth.net>
Subject: Re: [R-390] SPECIAL R390A PANEL (6kc & 8kc)

What about also doing a small panel with the markings screened onto it? Panel
you say? What is Tom talking about? Well, something similar to the blank panel
the R-725 has on the selectivity position, but with a hole for the filter switch.
Circular or rounded edge square, take the nut off the switch shaft and put the
plate on, covering the original markings for those of us with either engraved or
silkscreened panels You know how cheap some of us out here are! hehe

Probably mean making another screen though. :-( Of course the $135 for an
entire isn't bad.
Date: Sun, 13 Jun 2004 09:01:12 -0400
From: Bob Camp <ham@cq.nu>
Subject: Re: [R-390] SPECIAL R390A PANEL (6kc & 8kc)

With the stock audio chassis the 16 KHz filter isn't as useful as it might be. On a
radio running an improved audio chain the 16 KHz filter can be nice under the
right conditions. I wouldn't use it on a crowded band though ... The filter that
really does the major work around here is the 4 KHz on AM. It's about as
narrow as you can get and still get a usable signal. The real limit on what you can
do is finding the old filters in the right bandpass and impedance combinations.
IF deck tips                                     page 163

Date: Sun, 13 Jun 2004 10:05:18 -0400
From: "John KA1XC" <tetrode@comcast.net>
Subject: Re: [R-390] SPECIAL R390A PANEL (6kc & 8kc)

> With the stock audio chassis the 16 KHz filter isn't as useful .........

Or when tapping of the Diode Load output to a hi-fi amp and speaker.

>I wouldn't use it on a crowded band though ...

I like to use the 16 kc BW when monitoring 29.0 MC or so for activity, it increases
the chances of hearing something if the band opens.
Date: Sun, 13 Jun 2004 10:33:23 -0400
From: "Forrest Myers" <femyers@attglobal.net>
Subject: [R-390] r-390a chirping CW

I have a Capehart R-390 sn# 557 that is working quite well except for a couple of
problems. All bands and all filters work. There are a couple of problems though
and I'm asking the learned group on this list for any quick information or ideas.

Problem #1: Good clean CW signals chirp when heard on the 390a. It sounds
like the BFO changes frequency with AGC levels. Checking the voltage at the
audio module and it's a steady 150.1 volts. Haven't checked farther into it.

 Problem #2: Audio level is low but sounds good. I have to run the Local Gain
control wide open to get a comfortable listening level. This problem has crept in
over the past year. All tubes have been replaced. the radio has been re-capped,
including the filter capacitors in the audio module. It has been aligned and the
PTO is very linear after setting the end points. The rig works very well except for
the above mentioned problems. I've been away for about 9 months and haven't
used the rig. Am planning on getting into it again after building a set of test wire
extender so I can check into voltages and signals. Just thought I'd put out the
symptoms to see what advice I could gather.
Date: Sun, 13 Jun 2004 18:15:20 -0400
From: "James Miller" <JMILLER1706@cfl.rr.com>
Subject: Re: [R-390] r-390a chirping CW

I have found that replacing the first and/or second mixer tube may help the
chirp. Changing AGC on the mixer seems to cause it to load down the oscillators
as the AGC increases, pulling them off frequency slightly. Also could be another
suspect tube, maybe an osc. tube.
IF deck tips                                     page 164

Date: Sun, 13 Jun 2004 23:36:20 -0400
From: "James Miller" <JMILLER1706@cfl.rr.com>
Subject: Re: [R-390] r-390a chirping CW

Another thought: Check to be sure the 150V regulator tube is firing (it's
mounted on the audio module). If the VR tube is bad, the 150V line may not be
held constant, and changing AGC could cause it to change as the tubes pull
more/less current. I think the BFO (and maybe the PTO) is run off the 150 vold
line, so if it's changing a lot the BFO would tend to "chirp". Put a VTVM on the
159 line and watch it......
Date: Mon, 14 Jun 2004 15:39:27 -0400
From: JMILLER1706@cfl.rr.com
Subject: Fwd: Re: [R-390] r-390a chirping CW

This has taken on an interest to me because I have two 390a's here, one is a
Stewart-Warner, the other a Collins (almost). I notice a very slight "chirp" barely
noticable in the SW as AGC changes. However, it was much more noticable in
the Collins until I changed a mixer tube, ...it is lessened, but still noticeable,
maybe a tad more than the SW now (judging by ear). My theory was that the
AGC was pulling on a mixer tube, which then pulled more on one of the
oscillators causing it to "chirp". Changing the tube reduced it. I also observed
the +250 volt line which drives the xtal oscillators and other stages, and noted a
moderate change in its level as AGC changed (a change in AGC would cause all
controlled tubes to pull a varying plate load from that line). The 250V line in
both radios seemed to pull the same amount, but the Collins still show a little
more "chirp" as AGC changed. I would guess by ear to be 20-40 Hz. Is this
normal? Would be interesting to hear from others... turn your BFO onto a
strong, stable signal and run RF Gain up and down. ... you may notice a slight
pulling in beat note. Do others note this also?
Date: Mon, 14 Jun 2004 19:34:38 -0400
From: Jim Brannigan <jbrannig@optonline.net>
Subject: Re: [R-390] r-390a chirping CW

I had a problem with a 75S-3B that drove me crazy. On CW and SSB there was
distortion on the signals, AM was OK. It almost sounded like VHF aurora
distortion. I checked everything.... . a scope on all the oscillators..the whole
works....I tore apart the product detector circuits and no luck.....I put a CV-591 in
the IF chain and it was still there!!!! Finally I changed all the tubes, AGAIN.....and
it was gone.... Backtracking through the tube substitutions I discovered that the
PTO was FM'ing. This did not show up on the scope because I was using a signal
generator, and not an SSB or CW signal. In the end, I replaced all the
components in the PTO, except the coil. So far so good....
IF deck tips                                     page 165

Date: Mon, 14 Jun 2004 20:30:34 -0400
From: "Steve Hobensack" <stevehobensack@hotmail.com>
Subject: [R-390] r-390a chirping CW

I think the recomended way to copy cw is in MGC. Does the radio chirp in
MGC? (local gain high, rf gain adjusted for volume). If the set has an added
product detector or audio derived agc, it shouldn't chirp. (rf gain at max, local
gain adjusted for volume). You might monitor the pto canister output signal and
the crystal osc output signal and see if it chirps there.
Date: Mon, 14 Jun 2004 21:10:25 -0400
From: "Michael Murphy" <mjmurphy45@comcast.net>
Subject: Re: Re: [R-390] r-390a chirping CW

I wonder if the chirping R390A fixes bona fide chirp by undoing it? De-Chirping
in effect. Of course the chirp would have to be going in the right direction - like
upper side chirp and lower side chirp.
Date: Tue, 15 Jun 2004 10:24:20 -0400
From: "John KA1XC" <tetrode@comcast.net>
Subject: Re: [R-390] r-390a chirping CW

Not too unusual for radio's of this era when their RF gain is run wide open for
CW copy. My GPR-90 has the same chirpy phenomena which is minimized by
using SLOW AGC or eliminated by backing down the RF gain. Got to remember
these old radio's have free-running oscillators with no buffering between them
and their loads, and mostly unregulated supply voltages. Today's synthesized
radios will spoil you in this respect. John
Date: Mon, 05 Jul 2004 09:45:25 -0400
From: Bob Camp <ham@cq.nu>
Subject: Re: [R-390] filters needed

Assuming their web site is correct American Trans-Coil still has partial IF decks
for sale. They are at http://www.atc-us.com/ATCSHOP/ . Their web site is a bit
tough to navigate but the R-390 parts are hidden in there somewhere. The decks
they have are missing all the tubes, transformers and some of the under deck
stuff like the BFO coil. They do have all four filters on them and at the price they
have listed are probably your best bet if you need more than one filter. I have
dealt with them in the past and their stuff has always been as advertised.
Occasionally they have been a bit slow to take stuff down off the web site when
they run out of it.
IF deck tips                                     page 166

Date: Sat, 17 Jul 2004 13:04:14 -0400
From: "Vic/Johanna Culver" <vculver@verizon.net>
Subject: [R-390] Hang AGC Circuit

Sorry -- this originally sent to wrong address. I hope it doesn't duplicate. Hello,
Group. A really good friend gifted me this morning with something he said I
really needed for my R-390 -- a very competently built "HANG AGC" unit. Two
tubes, even!.

The information indicated that it was from a design published in 'the handbook.'
I assume this handbook is an older version of the ARRL Radio Amateurs
Handbook. Would anyone care to comment on the pro's and/or con's of adding
a hang AGC unit to a radio -- beyond the fact that some of us don't want
ANYthing that 'ain't stock.' Thanks, Vic
Date: Sat, 17 Jul 2004 16:49:10 -0400
From: Bob Camp <ham@cq.nu>
Subject: Re: [R-390] Hang AGC Circuit

The AGC in the R390 has a slower attack speed than more modern AGC circuits.
A number of people have done a number of things to change this. Probably the
most common way to go these days is to put a couple of solid state diodes and a
couple resistors in the AGC. The idea usually is to speed up the attack time and
leave the decay time where it is. The net result is an AGC that cuts in fast and
then drops out slowly. One term for his is "hang".

The solid state diode mods are no cut, no chop mods. They are easily reversed if
in the future you decide to go 100% stock. For that reason alone I would
recommend them over some of the earlier tube based designs that involved
more surgery to the radio. I do not know if the tube versions worked as well as
the solid state versions, but it is safe to say they did not work any better.
Date: Fri, 30 Jul 2004 14:02:05 -0600
From: "Mike Wells" <mwells@gcea.coop>
Subject: [R-390] Hello

I am new to the list. I just picked up a couple R-390A's last week and thought I
would see what sort of helpful pointers I could get. The receivers I picked up are
nice units. One is a Collins built unit and the other is a Capehart unit. I'm sure
that there has been lots of chatter about the 26Z5 rectifier tubes. I am in need of
one and started looking around and it appears they may be hard to find and
expensive. Is there a good source for them? I am also curious about the
calibration of the carrier level meter. I have adjusted the zero set point, however
with the two 390's setting side by side one registers a much higher reading on
the same signal, yet they both hear very well. Guess that only listening by ear
isn't a good sample so would you think its just an alignment problem?
IF deck tips                                     page 167

Date: Sun, 29 Aug 2004 09:07:47 +0100
From: Charles B <ka4prf@us-it.net>
Subject: [R-390] Notch filter

Is there any one add on that I can get to produce a notch filter function for my R-
390A. I don't want to modify the receiver. I have the QF-1A unit, but it's kinda
of old and I don't trust it.
Date: Sun, 29 Aug 2004 09:20:05 -0400
From: Bob Camp <ham@cq.nu>
Subject: Re: [R-390] Notch filter

As far as I know there is no way to do an internal notch filter on the IF of the 390
without significant modifications to the radio. The IF output is probably your
best bet combined with an external IF. In order to really do a good job with a
notch filter it's better if the filter is at the IF. Of course this is just the start of the
process. Since you now have the entire tail end of the IF outside the radio some
things have changed. The AGC now really should come from the external unit
and feed back into the radio. The 390 is at least set up for this part of the
process. I don't know of many boxes that are set up that way though....

The next thing is that the demodulator is now in the external box as well. That
makes the mode select switch on the radio nonfunctional. Finally feeding the
audio back into the radio is a little problematic. It can be done but it is not as easy
as it should be. A lot of the boxes just went ahead and did their audio. That takes
out the volume control knobs and audio filtering as well.

That's a lot of stuff just for an IF notch filter. But if you are still game, keep on
reading .....

Most of the good old IF notch filter designs worked with IF's around 50 KC or
so. They would mix down from 455 to a final low IF, filter, and then demodulate.
I do not remember any good notch designs that worked directly at 455. They
may be out there, but not on any radios I ever owned. If you go that way it's not
just a notch, it's an entire extra IF strip.

One thing that has come along since the R-390 was born is digital signal
processing. Most people look at this as a neat way to do filtering, but it's more
than that. The one thing that most DSP units do very well is adaptive notch
filtering. Properly done they also made good demodulators. You can do the
process at either audio or at the IF. The IF processing is better, processing at
audio is cheaper.

Of course if you are going to do it all at audio then there is another solution. A
lot of people use outboard audio filter boxes. The AGC does not work the way it
should and you still need some strange stuff with speakers. The one I happen to
like is the JPS NIR-10. They show up on various sites fairly cheap.
IF deck tips                                     page 168

If you want to go the IF route about the only source I know of for outboard
boxes is Sherwood Engineering. Their box works well with the R-390 and they
have good support for their products. It's a small market and I'm a bit surprised
anybody can afford to make new gear like this.

Now if you still are not satisfied there is the roll your own approach .... 24 bit
A/D's and 32 bit floating point DSP on an R-390. A little work with the good old
C compiler and you'd be in business. Think of the possibilities ..... we could name
it the R-390B
Date: Sun, 29 Aug 2004 11:12:33 -0500
From: Jerry K <w5kp@direcway.com>
Subject: RE: [R-390] Notch filter

Or, you could run your 390A audio into a Timewave DSP-599ZX like I do, have it
all in one neat little box, and still have a spare channel left over for an additional
Date: Sun, 29 Aug 2004 19:42:09 -0500
From: bw <ba.williams@charter.net>
Subject: Re: [R-390] Notch filter

The Heath HD-11 works very well as either a notch or a Q multiplier. Best of all,
it is tube gear using the 12AX7. I've had mine hooked up for a year now. They
are fairly cheap.
Date: Mon, 04 Oct 2004 18:00:22 +1000
From: Damien Vale <lcval1@netcon.net.au>
Subject: [R-390] IF module disassembly

I want to change C533 in the IF module but can't get at the base connection
without removing H243 which is part of the BFO pitch assembly. Are there any
problems associated with this? Although the set is working fine (a Collins 1955
series), C533 is covered with a white powdery material so I would like to change
it, and while I'm there the ones adjacent to it C534 & C538.
Date: Thu, 7 Oct 2004 14:05:13 EDT
From: K2CBY@aol.com
Subject: [R-390] IF module disassembly

None, so long as you keep track of which lead goes to which pin of the BFO
IF deck tips                                     page 169

Date: Thu, 07 Oct 2004 14:21:55 -0400
From: N4BUQ@aol.com
Subject: Re: [R-390] IF module disassembly

It's been a while, but as I recall, I removed the BFO when recapping my first
R390A for just the reasons you describe. Just solder the wires back to it as they
were and you'll be fine.
Date: Thu, 14 Oct 2004 12:51:51 +0800
From: face@netunltd.com.au
Subject: [R-390] r-390 Army manual mods


A QUERY: My manual is the Army version TM 11-856A (stamped ME 147+ O2a
inked in) Jan 1956. (odd that it came with a supposedly NAVY R-390A !) It has
been much annotated and seems to have been used for shop maintenance work.
There are inked in additions to the diagrams and some typed inserts replacing
'x' d out pictiures.

QUERY: I have a page (original page from a different manual) inserted between
pages 108 and 109 (covers Fig 64 .. IF sub chassis, top view and Fig 65, bottom
view.) The inserted page (is) pages 3 , obverse 4 , showing the same sub chassis,
but with obvious photo differences. The inserted page has the reference 'TAGO
6903A ' on the bottom. The photo references are TM856A-34 and TM856-35
(original manual) and on insert TM856A-C4-1 and TM856A-C4 ??? (final bit
obliterated by cigarette burn... so used as maintenance manual for sure!)
 The insert shows some major differences to the original layout..Example: It
shows a bunch of 4 trimmers on FL502 marked C513,C358, C571, C512. When I
can get another more abled body body to help me take my R-390A out of its
rack,(got no slides) I will then see if mine looks the same. Until then, can anyone
tell me the relevance of this , please ?.

i.e. Are the added trimmers a later and necessary mod ?
    Are there differing versions of the mech filters / and or tuning methods in
these things? (I have an IF alignment sweeper somewhere that doesnt load
things much when hooked up.. looks like I may have to use it .....is sweeping the
IF the best way to align ? .. usually is)

ADDENDUM: Seems its likely all this has been reviewed by you guru's before
... To save everyones time re cycling the wheel, if there's previous links to any
of this, how do I get on to them? (I'me an internet novice).
IF deck tips                                     page 170

Date: Sat, 30 Oct 2004 14:07:55 -0400
From: "David C. Hallam" <dhallam@rapidsys.com>
Subject: [R-390] R-390 Problems

I have a problem with my R-390 nonA and don't know exactly where to start.
The radio went dead. I suspected a B+ problem and found that one of the
26Z5W rectifiers had gone bad. I replace both and now can measure 180 VDC at
the test point for regulated B+. The radio still is dead. Symptoms; (a) no
movement in either the line audio or carrier level meters on any band with
either manual or automatic gain and ....(b) no noise on the local audio output at
any setting of the audio gain control

455 kHz signal from my URM-25D applied to test point E210 (grid of the 3rd
mixer) produces the expected output measured with the 410B at the diode load
terminal until the pass band is increased to 8 kHz or 16kHz. Then it's like
something breaks into oscillation as the diode load voltage increases to
something like 100 or more volts.

I guess the next step is to start checking the voltages at each tube, but I
wondered if someone might have an idea as to a specific location to concentrate
Date: Sat, 30 Oct 2004 14:50:16 -0400
From: Bob Camp <ham@cq.nu>
Subject: Re: [R-390] R-390 Problems

Well the first thing to *always* be sure of any time you see IF filters involved is
to be sure that the "magic" B+ blocking capacitor is in series with the filters. I see
no reason why that would be your problem but it never hurts to be sure. The
26ZW5 can get pretty dead and the radio will still work. I suspect yours has been
dead for a while and you just found the problem when the second issue started
up. As you may have guessed the problem is likely to be an IF stage going into
oscillation. Since it changes with the filters it probably is one of the stages ahead
of the mechanical filters. I would also do a resistance check on the filters just to
be sure the two wide band filters are still ok.
Date: Sun, 31 Oct 2004 08:02:32 -0500
From: "David C. Hallam" <dhallam@rapidsys.com>
Subject: [R-390] R-390 Problems Update

Thanks to all who replied to my request for help. The problem turned out to be
a failed ballast tube. I changed the VFO and BFO tubes to 12BA6's and stuck the
paper clip jumper in the ballast tube socket. All is working well again. I don't
know if the failure of one of the 26Z5W rectifier tubes precipitated the failure of
the ballast tube or if they were two unrelated malfunctions. The rectifiers were
replaced with a pair of Ted Weber's copper top silicon plug in's.
IF deck tips                                     page 171

Date: Sun, 31 Oct 2004 09:40:10 -0500
From: "David C. Hallam" <dhallam@rapidsys.com>
Subject: RE: [R-390] R-390 Problems Update

I replaced the 6BA6's in the VFO and BFO with 12BA6's, which eliminates the
need for the resistor to replace the ballast tube.

There has been a recent discussion on this list about the ballast tube and ways to
replace it. I think the general consensus is that the ballast tube really is not
needed to stabilize the VFO unless you looking for the last little bit of stability. If
so, you need to replace the ballast tube with something more sophisticated as
given the relative "stability" of the AC line, the ballast tube doesn't do much in
that regard.

Replacing the VFO and BFO with 12 V filament tubes is one of the suggested
Date: Tue, 23 Nov 2004 10:45:36 +0000
From: Charles B <ka4prf@us-it.net>
Subject: [R-390] BFO Pitch

I had the IF subchassis out of my R390A last week to check underneath to see if
there were any problems i.e. burnt resistors etc. There weren't. Anyway, I had
inadventently turned the BFO Pitch shaft when it wasn't hooked up and
consequently I think my pitch maybe off. Anyone know the proper procedure
for adjusting the Pitch WITHOUT instruments before connecting it back onto the
Date: Tue, 23 Nov 2004 03:41:50 -0800 (PST)
From: "KC8OPP Roger S." <kc8opp@yahoo.com>
Subject: Re: [R-390] BFO Pitch

Tune in a known freq station, WWV works good. If your dial is set right it
should read XX.000 depending on the freq. Tune for max carrier level at the
lowest bandpass possible to make sure your centered on the freq. Turn on the
BFO and zero beat. Should be 0 on the BFO dial.
Date: Tue, 23 Nov 2004 09:27:57 -0800
From: "Kenneth G. Gordon" <kgordon@moscow.com>
Subject: Re: [R-390] BFO Pitch

What has always worked pretty well for me is to set the selectivity at one of the
narrower positions, but usually not the narrowest, tune in a place with NO
SIGNALS, turn the BFO on, turn up the RF and AF gain so I can hear a lot of
band hiss, and adjust for lowest pitch.
IF deck tips                                     page 172

Date: Fri, 10 Dec 2004 00:31:17 -0500
From: Bill Abate <wabate@dandy.net>
Subject: [R-390] AGC problem

My 390A is almost finished its restoration. Looks pretty good and works well.
Well, except for SSB reception. If I try to tune in a ssb signal I get a lot of
distortion in the audio and the signal can't be tuned in properly. If I try the old
method of max audio gain and reduced RF gain, all is well. Of course this is not
the way other R-390A's work. BTW, AM reception is pretty good but has some
distortion in the audio.

I figured that the AGC was not working properly so I ran the AGC test in the
manual. I adjusted the ,local audio for 1.7V of audio with 5 microvolts of RF. I
then increased the RF sig gen to 1000 microvolts and the audio output went to 20
volts. It's supposed to increase to 3 volts, so I found the problem. The problem is
I can't seem to find the cause. I have AGC voltage on pin 2 of v506 (AGC line). I
got these AGC voltages with my sig gen:

5 mv ->         .04VDC
50mv ->          -.2 VDC
500mv ->         -3.8 VDC
5000mv ->         -7.1 VDC
50000mv ->         -9.6 VDC

I also found the AGC voltage on all the tube grids it was supposed to control.
The only thing I can conclude is that the AGC voltage is insufficient but the
manual does not say what the voltage should be with varying inputs. At least I
could not find it. I also tried slow, med and fast AGC and the results were the
same. Anybody have data on the AGC line? Any ideas as to the cause??
Date: Fri, 10 Dec 2004 02:42:30 -0600
From: "Bill Hawkins" <bill@iaxs.net>
Subject: RE: [R-390] AGC problem

Don't have voltages for you, but here are a few ideas: Do you have the right
tubes? No sharp cutoff where they should be remote cutoff.

Does the S meter read correctly?

Do the resistors in the AGC circuit have the correct measured values? How
about the cathode resistors of the controlled tubes? They should be within 20%
of the schematic value.

Is the resistance to ground of the AGC line greater than 100 meg if you isolate
the line? Can you measure the resistance with something that applies 20-30 volts
to the line? Or just apply voltage to the line with three 9 volt batteries and see if
it propagates down the line correctly.
IF deck tips                                     page 173

Date: Fri, 10 Dec 2004 09:34:26 -0500
From: "JamesMiller" <jmiller1706@cfl.rr.com>
Subject: Re: [R-390] AGC problem

AGC voltage for the front end RF Amp tube exists on the tuning shaft for the
antenna trimmer ... if there is oil or grease on the fiber coupler and washers
associated with the antenna trimmer, the oil could show as a path to ground for
the AGC voltage at this stage. This can reduce AGC effectiveness for the front
end. Spray with a non-oil based degreaser cleaner such as Big Bath. I have also
found that sometimes the .005 bypass capacitors at the AGC points throughout
the radio can go bad and pull down the line. I have had to literally replace all of
them in one radio. Finally, AGC is developed in the IF Module ... there is a
tuning coil there that looks like an IF can Z-something, I forget the number) that
you have to tweak to get the right AGC action.
Date: Fri, 10 Dec 2004 11:49:41 -0500
From: Roy Morgan <roy.morgan@nist.gov>
Subject: Re: [R-390] AGC problem

Have you set the IF Gain setting?
See: http://www.r390a.com/; and in particular:
Date: Fri, 10 Dec 2004 12:42:13 -0500
From: "James Miller" <JMILLER1706@cfl.rr.com>
Subject: Re: [R-390] AGC problem

I read your original post again, where you said "this is not the way others work...
" I have one 390a (a SW mfgr) that handles SSB pretty well at high gain. I have a
Collins 390a that doesn't do well at high gain, on SSB, but works well otherwise.
But I think the 390a that handles SSB without distortion is not the norm. Your
receiver may be just fine and working normally, since you say it is OK when the
RF gain is reduced. There are some AGC mods on the web that can help, one
simple one uses a couple of diodes in the IF deck. But in general I think that a
390a that distorts on SSB at high gain is normal. Just my opinion..
Date: Fri, 10 Dec 2004 12:33:42 -0600
From: Jerry K <w5kp@direcway.com>
Subject: RE: [R-390] AGC problem

I second that. I'd guess your 390A is probably working just fine. Both of my
390A's ('63 Teledyne/Imperial, '67 EAC) copy SSB wonderfully well with the BFO
set correctly and the RF gain at about 7 or so. Crank the gain all the way up and
it's distort city. So what? If I wanted a hands-off SSB receiver I would look to
Japan or Tennessee for it. It also wouldn't weigh 85 pounds, wouldn't have
anywhere near the mechanical/electrical "cool factor", and if it broke I'd have to
pay a small fortune to mail it to the manufacturer to get it fixed. Where's the fun
in that? :-)
IF deck tips                                     page 174

Date: Fri, 10 Dec 2004 14:11:29 EST
From: DJED1@aol.com
Subject: Re: [R-390] AGC problem

My TM 11-856A has a graph of AVC voltage versus signal level which you can
compare with measured results.

It shows about -2V at 10 microvolts in, -3.5V at 100, -6.5 at 1000, and -9V at
10,000. This depends on having set the receiver IF gain per the manual. I
haven't seen any data on how flat the AVC response is, but I know my receiver
audio output increases several dB as I increase the RF input by 40 or 60 dB. Let
us know what you find. I'm going to make some measurements and see how
well my AVC works.
Date: Fri, 10 Dec 2004 13:34:30 -0600
From: "Cecil Acuff" <chacuff@cableone.net>
Subject: Re: [R-390] AGC problem

Well I figured it would come up so I'll go ahead and bring it up...is that 10uv at 50
ohms input or 120 ohms. I'm guessing 120 but our generators are nearer 50.
Where's Bob Camp...
Date: Fri, 10 Dec 2004 15:55:11 -0800 (PST)
From: Joe Foley <redmenaced@yahoo.com>
Subject: Re: [R-390] AGC problem

Don't look at me I was reading this new website:
Date: Sat, 11 Dec 2004 00:55:56 -0500
From: Bill Abate <wabate@dandy.net>
Subject: Re: [R-390] AGC problem

OK guys, thanks for the info. First off I have the gain pot a little on the low side
for a better s/n ratio. If anything that should help. My sensitivity is between 0.6
and 1.1 microvolts for 10 db s+n/N. All the tubes are correct and have been
tested in a Hickok before aligning the rig. It really is perking quite well. I have
that darn linearity adjustment to do for the Cosmos PTO, but I got sidetracked
on this SSB thing.

I pulled the IF deck and played around with it for most of the day. I replaced a
few resistors and caps but not because they were that bad. Same results.

I got one more piece of data that makes no sense. The suppressor grid of V504
and V508 (pin 2) has +6 V on it instead of the -2.5 that should be there according
to my manual. The voltage does not change with AGC or MGC selected with
the function switch so I conclude that it is coming from V509 and not the AGC
bus itself. Now the no signal voltage on pin 1 or 2 of V509 is -.5 V and should be
IF deck tips                                     page 175

-1.9 V. Maybe that is why I am not getting the AGC voltages that Ed, WB2LHI,
said his manual indicates.

One thing that I think has helped is to lower the B+. The military put diodes in
the place of the 26Z5's and the voltage was 255 which is a little high. I inserted a
10W 40 V zener and got the voltage down to 215. The distortion is not that bad
now. I can copy some stations with full RF gain but it still does not have good
fidelity. Maybe I moved the overall gain of the rig to where the AGE has more
of an effect? I am still blaming the AGC voltage. Z503 has been peaked but
maybe there is something wrong with it? Not ready to give up yet.
Date: Sat, 11 Dec 2004 03:05:27 -0500
From: "James Miller" <JMILLER1706@cfl.rr.com>
Subject: Re: [R-390] AGC problem

Get the ohmmeter and check the values of all resistors, replace any out of spec.
ones. Start with the IF module. The old carbon resistors tend to drift higher as
they age. Especially check cathode, plate and screen resistors (they tend to
change from being in the line of power flow). The resistor aging problem is
more common than you would think. They can "look" good cosmetically and
still be very bad.
Date: Sat, 11 Dec 2004 03:09:15 -0500
From: "James Miller" <JMILLER1706@cfl.rr.com>
Subject: Re: [R-390] AGC problem

One more suggestion: Tighten all the hardware, screws, nuts, etc.especially
those that hold the tube sockets and ground lugs down. Again, they loosen with
age due to heating/cooling cycles. And don't discount a few cold solder joints or
even joints where the mfgr forgot to solder and QC. I had an IF deck by Clavier
once where at least 5 pins had absolutely no solder on them at all. Anything can
Date: Sat, 11 Dec 2004 09:36:44 -0600
From: "Cecil Acuff" <chacuff@cableone.net>
Subject: Re: [R-390] AGC problem

Bill you are trying to make a SSB radio out of one that was never designed to be
one. I have never seen an unmodified R-390A that would copy SSB with the RF
gain full up...it wasn't designed to do so. Most require that the RF gain be
reduced several notches to get any kind of decent demodulation of a SSB signal.
That's why all the modification information over the years such as the "Langford
AGC" mod etc..... It's an age old problem. It sounds like your radio is working
properly....with some voltage readings that are out a bit. What are you using to
measure them? Needs to be an old not so high tech analog style meter. One
that loads the circuit a bit. That is what was used when the readings were
documented. Something like an old Simpson 260 would be in order I would
think. Other can comment on that as well...
IF deck tips                                     page 176

Date: Sat, 11 Dec 2004 21:01:13 EST
From: DJED1@aol.com
Subject: [R-390] AGC problem

I made a few measurements on my receiver to see what the AVC characteristic
was. I got the following curve, which shows pretty good AVC action:

microvolts in             AVC volts             audio level
5                         -1.0                      -5 dB
50                        -4.0                      -3 dB
500                       -7.0                      -2 dB
5,000                     -9.4                      -2 dB
50,000                    -12.3                     -3 dB

I was also curious about the input impedance match to the generator, so I put
my MFJ antenna analyzer on the receiver input. Interestingly, all readings at
center frequency were in the range of 25 to 50 ohms, with the reactance being
tuned out by the antenna trimmer. I suspect I may have a bad measurement
because the signal level is so high. Has anyone done a similar measurement? Is
the receiver input really 100 ohms or so, or have we been worrying about
generator mismatch for nought?
Date: Sun, 12 Dec 2004 16:56:49 -0500
From: Bill Abate <wabate@dandy.net>
Subject: Re: [R-390] AGC problem

My AVC voltage at 5 and 10 mv does not agree with yours. It is less. 10mv
shows -0.25. Can't figure anything to increase it. The high end is OK. Resistors
and caps have been replaced. SSB reception is still distorted but not as bad as
when I was running 255 VDC B+. My friends 390A receives SSB at full RF gain
and sounds good. Maybe I can swap radios when he isn't looking! :)

I won't bother you guys further with this as I think this is as good as I'm going
to get it. At least I was able to get the radio to meet the AVC spec in the manual
so something was accomplished. I may experiment with the gain adjustment pot
to see if that helps. I believe it is IF gain causing the problem and not RF gain.
Next year's problem. On to the Cosmos PTO!
IF deck tips                                     page 177

Date: Tue, 14 Dec 2004 19:17:09 -0500
From: Bob Camp <ham@cq.nu>
Subject: Re: [R-390] AGC problem

Sorry to be late on this one.... I think the AGC side of this has been pretty well
worked over. There is another side to this though. The distortion on SSB
detection is related to the way the BFO works as a detector. It distorts when the
RF signal gets to high for the way it's set up. One of the things that directly
affects this is the level of the BFO voltage injected into the detector. Since the AM
detector diode gets used as a mixer when the BFO is running it's characteristics
also get into the act. Some 390's have been modified to increase the BFO injection
and some have some detector tubes in them that have gotten a bit soft. In this
case a soft tube *might* work better than one that's up to spec. I would also
agree that most R-390's do not work very well on SSB with the RF gain turned all
the way up. If I was going to look for something odd I would take a look at the
radio that picks up SSB fine rather than the one that has problems.
Date: Wed, 15 Dec 2004 15:42:22 -0500
From: "Drew Papanek" <drewmaster813@hotmail.com>
Subject: [R-390] ACG problem

>SSB reception is still distorted but not as bad as when I was running
>255 VDC B+. My friends 390A receives SSB at full RF gain and sounds
>good. Maybe I can swap radios when he isn't looking! :)

Perhaps you and your friend could swap IF (or other) modules for test purposes-
that would certainly help pinpoint the location of any circuit fault. You could
take voltage measurements at various points on the substitute module and
compare with those taken from your module. Maybe your IF module would
provide the desired SSB reception in his radio, telling you that the problem lies
elsewhere in your radio.

On the same topic Bob Camp wrote:

(excerpted) >Some 390's have been modified to increase the BFO injection and
some have
>some detector tubes in them that have gotten a bit soft. In this case a
>soft tube *might* work better than one that's up to spec.
>I would also agree that most R-390's do not work very well on SSB with the
>RF gain turned all the way up. If I was going to look for something odd I
>would take a look at the radio that picks up SSB fine rather than the one
>that has problems.

Bob brings up some very good points. Again, module swapping or even tube
swapping (from the other radio) could provide clues. About B+ voltage: Bill's
255v seems a bit high even for a radio with 120VAC power and no B+ reducing
devices. Where was the B+ measured? At the
IF deck tips                                    page 178

rectifier cathodes is not a good place because the large ripple voltage there
would confuse many DC meters, giving inconsistent/inaccurate readings. A
better place would be at the filter caps (remember, the filter is choke input). The
screen of the audio output stage (either Line or Local) is convenient-yank the
6AK6, wrap a wire around the appropriate pin and plug back in. The wire can
be left in place to provide a convenient B+ shock hazard :)

I measure 180 volts B+ at the 6AK6 screen with 120VAC power supply input and
200 ohms in series with the rectifier common cathode lead (solid state diodes).
Date: Thu, 16 Dec 2004 22:24:07 -0800 (GMT-08:00)
From: Tony Angerame <tangerame@earthlink.net>
Subject: [R-390] Re: R-390 Digest, Vol 8, Issue 11

Let's not forget about the "Dallas lankford" ssb agc mod. It consists of adding a
voltage doubler (Two Diodes) to the agc line. The faster action (attack) of the
solid state devices and the increased agc voltage allow one to operate with the rf
gain all the way up. I use it with an outboard selective rf voltmeter which has a
product detector for excellent ssb. He also had a way to increase bfo injection to
make the diode detector more acceptable. I think the old timers must be tired of
responding with this answer so offically being old myself I took up the yoke.
Date: Fri, 07 Jan 2005 08:49:03 -0500
From: Gord Hayward <ghayward@uoguelph.ca>
Subject: Re: [R-390] AGC Cap

I wouldn't use an electrolytic. At the best the ones I've seen have a tolerance of
+80/-20% and they leak. It would be like putting a resistor across the AGC! I did
find a suitable substitute - I think its either 1 or 2 polycarbonate caps which give
a replacement smaller than the metal box in there now. I put them in a box of
stuff waiting to be installed when I pull the set out of the rack. I have a few
things to do but currently, if it ain't broke, I ain't fixing it.
Date: Fri, 7 Jan 2005 09:50:12 -0800
From: "David Wise" <David_Wise@Phoenix.com>
Subject: RE: [R-390] AGC Cap

What Gord said. Even a new electrolytic will leak about as much as your bad old
oil/paper cap. The new cap *must* be "no"-leakage, for example any of the
plastic film varieties. I suppose ceramic would be up to the job, but I've never
seen one at 2uF/400V. It would be quite a lump! I replaced mine with a small
AC motor cap, again with a plastic dielectric. It fitted easily in the original can
after gutting. That's not a pleasant job, but since it wouldn't fit under the chassis
it was my only choice. When cruising, the cap won't see more than about 200V,
but if you have a SS power supply there will be more during warmup but not
more than about 350 for sure. Since cap life depends more on cruising voltage
than transients, even a 400V cap will last for generations.
IF deck tips                                    page 179

On a related note, I breadboarded my anti-moment-of-silence mod, and it looks
good. As expected, 0.15uF is the optimum value if you like the old time constant.
0.1 and 0.22 are perceptibly off. Next week I'll do quantitative measurements.
I'll modulate the signal generator with a slow square wave, and watch the AGC
line on a scope.
Date: Sat, 8 Jan 2005 15:10:29 -0800
From: "ELDIM" <eldim@att.net>
Subject: Re: [R-390] AGC Cap

Is that AGC Cap an metal encased OIL BATHTUB with mflange mtg holes on
each side? Or, is it a plain axial lead type? I know I have many here in the
inventory. What was the Part Number? I concur, that using an electrolytic is not
a good solution.
Date: Sat, 08 Jan 2005 18:41:29 -0500
From: Bob Camp <ham@cq.nu>
Subject: Re: [R-390] AGC Cap

The AGC cap is an oil in metal type. I don't think it's a standard one though.
Given the state of most of the oil and paper caps it's probably best to replace this
one with a plastic insulation part. Popcorn noise on the AGC line is the last thing
you want to have.
Date: Thu, 20 Jan 2005 16:19:45 -0800
From: "David Wise" <David_Wise@Phoenix.com>
Subject: [R-390] Ending The Moment Of Silence

I did it! I have perfected a mod that eliminates the carrier level disturbance when
switching the R-390/391/390A AGC rate. Only the front panel wiring changes. It
is 100% compatible with standard IF decks and those with the Lankford AGC
mod. This is how Collins should have done it, it would have cost them next to
nothing. Like the carrier level pot, the engineer just didn't think it through. The
mod I posted earlier had side effects that ultimately caused me to reject it,
although it was very compact and easy to do. This mod borrows an idea, but
otherwise it's totally new. I have tested it extensively, and the ergonomic
improvement is just fantastic. You'll never realize how obnoxious and fatiguing
the stock AGC switch is until you try this.

    No more "Moment Of Silence" (SLOW to MED)
    No more blasting (MED to SLOW)
     Same time constants as before, or season to taste
    Compatible with existing modules
    Reversible (no holes)
    No "box on the side", it's all internal
    Works with decks that have a bad C551
IF deck tips                                     page 180

   Needs a new AGC switch (2-pole vs 1-pole)
   Needs a piece of sheet metal (if you want it to be neat)

    FAST-MED: Dip, Nothing, or Surge, depending on signal levels
    MED-SLOW: Severe Overload for 1-2 seconds
    SLOW-MED: No Signal for 1-2 seconds
    MED-FAST: Nothing

      FAST-MED: Nothing!
      MED-SLOW: Nothing!
      SLOW-MED: Nothing!
      MED-FAST: Nothing

(Lest someone accuse me of advertising hype, I will qualify the above claims to
the extent that at very high signal levels (over 80dB), you may detect a slight
surge on MED-SLOW and SLOW-MED, but it's barely perceptible except under
artificial laboratory conditions, where it becomes merely "perceptible".)

Cost: About $15 and a couple of hours. Well? Dave Wise
Date: Thu, 20 Jan 2005 20:13:00 -0500
From: Bob Camp <ham@cq.nu>
Subject: Re: [R-390] Ending The Moment Of Silence

Only the obvious question - Is it easily reversible ?
Date: Thu, 20 Jan 2005 21:21:00 -0600
From: "Cecil Acuff" <chacuff@cableone.net>
Subject: Re: [R-390] Ending The Moment Of Silence

You have found a way to eliminate the only internal self test besides the Xtal
Calibrator the R-390A possesses? I'll have to think about that one....
Date: Fri, 21 Jan 2005 09:17:46 -0800
From: "David Wise" <David_Wise@Phoenix.com>
Subject: RE: [R-390] Ending The Moment Of Silence

Sorry all, I have an emergency at work today and won't have time to write
much. I did think of a couple of "Pro"s I forgot yesterday:

      No semiconductors
      No active components
      No hard-to-find or exotic components

> Is it easily reversible ?
IF deck tips                                     page 181

Depends on what you mean by "easily". It's not a plug-in like my 3DW7. You'd
have to drop the front panel, unsolder three wires, remove an assembly and the
new S107, remount the old S107, and solder three wires.
Date: Fri, 21 Jan 2005 15:50:09 -0800
From: "David Wise" <David_Wise@Phoenix.com>
Subject: RE: [R-390] Ending The Moment Of Silence

It's nothing scary, just a flat bracket to base a terminal strip on, to avoid gluing
or drilling a hole on the front panel.

I didn't see any real mount points where there was also enough room for the
strip + components. I'm going to try to put it all into an HSN article.
Date: Sat, 22 Jan 2005 09:14:35 EST
From: DCrespy@aol.com
Subject: Re: [R-390] Ending The Moment Of Silence

Dave, and all. I should still be a subscriber and have not seen a copy of HSN in
at least 2 years. I think it has died a quiet death?

Please consider some other way to make the info available?
Date: Sat, 22 Jan 2005 08:00:56 -0800
From: "David Wise" <David_Wise@Phoenix.com>
Subject: RE: [R-390] Ending The Moment Of Silence

I've talked to Barry Hauser. It's been in suspended animation, but this is a good
candidate to jump-start it. If that doesn't happen, be assured that the details will
surface here. My announcement was to gauge your interest, as previous
offerings didn't generate much enthusiasm. Controversy, yes :) In the mean
time, if there's an R-390/391 nearby, or someone has some high-resolution or
close-in photos that show the top rear area of the front panel and its relation to
the rest of the set, I could predict whether there's room to fit the mod there. It
can go anywhere, but front panel top-center is the "sweet spot". I hate trailing
Date: Sat, 22 Jan 2005 08:03:31 -0800
From: "Kenneth G. Gordon" <kgordon@moscow.com>
Subject: Re: [R-390] Ending The Moment Of Silence

Try Electric Radio. They are really good people and gladly would take such an
article. Go to http://www.ermag.com/ and get hold of the editor.
IF deck tips                                     page 182

Date: Sun, 13 Mar 2005 11:24:24 EST
From: Flowertime01@wmconnect.com
Subject: [R-390] Bad AGC

I do thank you for the article. Would you know it. My R390 started behaving
just as you describe. It works good in the Manual AGC mode and looses all gain
in the AGC mode. I had been looking at the AGC sections looking for a cap that
would short after it warmed up and not finding any thing. Now I have some
place to go looking for the cause, and a real solution (new filter) when I find my
exact problem.

I was still employed a while back and went on the road doing first article testing
for a new Navy Ship. I watched engineers at several independent laboratories
abuse some serious computer network equipment to qualify it for use aboard
Navy ships. I had to give up the R390 net here as I was over extending my
computer usage. But now I retired, moved from San Diego California to
Westminster South Carolina. Maybe now I can talk to Hams In San Diego. I used
to live in Spring Valley a bed room community about 10 mile from down town
San Diego. I have radio contacts from Japan, Texas, Maine, Washington State and
British Columbia, from Spring Valley. I knew every one in the El Cajon Radio
Club, and never worked any one in San Diego. I love the aspects of antenna
propagation. As soon a we finish moving in and I get the toys unpacked, I'll get
back on the Air. Most likely I should ask the FCC for a new call and give up my
old California KC6TRU call. The R390A is still packed. I had a good scope get
crushed in the move, but every thing else survived. A here I am, the first day
back on line and Al has nailed a problem that I have been pondering for some
Date: Fri, 01 Apr 2005 18:32:33 -0500
From: Bob Camp <ham@cq.nu>
Subject: Re: [R-390] Help getting unstuck!

Well a large pipe wrench attached to the appropriate allen wrench, maybe
combined with a five pound sledge probably would get it moving. The obvious
problem is that almost anything past normal pressure with a standard tuning
tool is likely to shred the coil rather than moving the core. There is almost no
reason to believe that moving the core is worth damaging the coil. Even if things
are a bit out of alignment the radio probably will work perfectly well as it's set.

Often the problem is that the coil form has shrunk over the years and now it's
simply to small for the core to move in. In that case it may need *more* not less
humidity to be fixed. I have never had any success at "steam treating" in this
situation but it's been recommended in the past.

Another idea is that you have crud in the threads. In order to get things moving
you need lubrication. The punch line here is to use a light weight oil to free up
the core. To me that sounds like an excellent way to destroy the core and or the
IF deck tips                                     page 183

coil. I would not try it on one of my radios. Another recommendation is to use
spray on contact cleaner. I have tried that one and it didn't work on my coils.

I realize none of that is much help at all. The main point is that this may be one
where simply leaving it as is makes the most sense.
Date: Fri, 1 Apr 2005 17:11:16 -0800 (PST)
From: Joe Foley <redmenaced@yahoo.com>
Subject: Re: [R-390] Help getting unstuck!

Try some freeze spray on it, but take the cover off first to you can watch to see
that you don't turn the coil instead, that may pull the wires off. Try just blowing
some air from the compressor in it first, maybe it will dislodge some of the crud.
Date: Thu, 31 Mar 2005 22:44:11 -0500
From: "Michael Murphy" <mjmurphy45@comcast.net>
Subject: Re: [R-390] Help getting unstuck!

You need a can of slugout. You said that just the top core is stuck in T-501. Could
have been worse - it could have been the bottom coil.

First adjust T-502 and the bottom coil per the instructions

I liked all of Bob's ideas that did not work of course. What about using his light
oil idea and then heating an allen wrench red hot and sticking it in just to see
what would happen. Then follow up with the cold spray (or a fire extinguisher).

Next take your not so favorite hex tuning stick and coat the end with Zap a Gap
Cyanoacrylate. After you stick that in and let it set up, something should move.
When you are happy, saw off the end of the stick and glue on a small knob. Now
you can tune the coil casually. Like he said, this is a broad tuned coil. Probably
good enough to just leave it.
Date: Fri, 1 Apr 2005 23:37:52 EST
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] Help getting unstuck!

>Can't seem to get the top slug in T501 to move. Craig,

Sounds like a chance to stop and test. Run the 455 into the IF deck and do a signal
to noise test. If you can get a 28 to 1 signal to noise the coil is close enough and
effort to adjust the stuck slug will exceed return on investment. If its close just
leave it alone. If its not close then maybe you will be loosing some fidelity in the
16K band width.

Use the Adjustment of Gain Adj Potentiometer. Paragraph 73 in TM 11-5820-358-
35. you want to run 150 uv of 455 into the IF deck. set the gain adjust for -7 volts
on the diode load. With 30 percent modulation you should get about 0.5 watt of
IF deck tips                                     page 184

audio across the 600 ohm output. We metered the headphone output with a test
lead that ended in a phone plug. You can meter dB with most analog AC volt
meters and the instruction book (page of paper) for the meter.

Turn the signal generator modulation off. Now you have just a 455 carrier signal.
The audio output should have dropped 30 dB and there should still be -7 volts on
the diode load.

If you cannot get 30 dB signal to noise here, start swapping tubes around and
trying to do some alignment. Trouble is there is no easy way to determine if
your IF deck was stager tuned or aligned at 455.

So try to perform the stager alignment procedure as detailed in the TM first.
If you are loosing gain, go for the straight alignment.

Just leave the stuck slug for the very end. Get all the other bugs out of the way

Get good tubes in and do the best alignment you can get other wise.

If you get up to about 28 to 1 just leave that stuck slug alone.Only after you get
everything else as best you can and you know by measurement that the IF deck
is not up to minimum then get worried about that slug.

Get the cover off the can so you can see what's moving. The hot air hair dryer is
the least offensive way in. Most of the time it will melt down some of the wax.
Heat and soften the gunk.

You can get an IF deck from Fair Radio less crystal filters and tubes, and BFO and
ballast tube. It will have a T501. The IF cans (T501, T502, T503) are all the same.

Push comes to shove and you conduct a destructive test, ask here on the
reflector, someone likely has the part stuck on some of there collected spare
parts and would make you an offer your not likely to refuse.

Good luck and be gentle. Roger KC6TRU
Date: Sat, 2 Apr 2005 13:50:31 -0800
From: "Craig C. Heaton" <wd8kdg@worldnet.att.net>
Subject: RE: [R-390] Help getting unstuck!

Taking a real close look at the top slug, cleaning the top, it does have a crack. So
its not going to move as one piece. Cecil's idea of a root canal might be the best
option if the receiver will not come up to specs. I'll use this as an excuse to put
out a general call for parts n' pieces! If someone has a spare slug, T501, or a IF
sub-chassis please drop me a line.
IF deck tips                                     page 185

The Motorola will never be a museum piece, but it would be nice if everything
would work as designed. In the coming days, I plan to go through the entire
receiver and at some point will be able to try the signal to noise test.

Took the IF sub-chassis out last night and looked at what it would take to replace
T501, lots of work. Root canal would save time vs the soldering iron to replace
the entire transformer.
Date: Sun, 03 Apr 2005 07:55:17 -0400
From: Barry Hauser <barry@hausernet.com>
Subject: Re: [R-390] Help getting unstuck! - Call for Mr. ATC

Unfortunately -- no IF coils/transformers. Those were harvested and sold off a
long time ago, well, before I got involved. The IF decks have all four filters, but
no IF cans. Most of what's there is still on the ATC site (http://www.atc-
us.com). Click on the cascading drop-down menus to look around.

I'd suggest contacting Phil at Fair Radio. They often sell individual parts which
they pull off parts modules as needed and which are not necessarily listed in the
catalog or website. Further suggest waiting until you have a replacement in
hand before getting any more aggressive with that stuck core. As someone
pointed out (maybe Bob), it's broad-tuned and may well be fine set the way it's

Date: Sun, 03 Apr 2005 12:14:26 -0400
From: Bob Camp <ham@cq.nu>
Subject: Re: [R-390] Help getting unstuck! - Call for Mr. ATC

The 17 MHz crystal is still available from the normal crystal supply guys. You
probably can get them at a better price from Fair though.
Date: Sun, 10 Apr 2005 14:00:48 -0500
From: "Barry" <N4BUQ@aol.com>
Subject: [R-390] 1.0 and 0.1 filter settings

Can someone give me the "Reader's Digest" version of how these two settings
work in an R390A? I'm working on restoring the modules for my newest
project. After replacing C553 (just to be safe), I plugged it in place of the IF deck
in my working R390A. It seems all four filters are working; however, when I
switch to 1.0 or 0.1, the signal disappears almost completely, no matter how
closely I tune to the frequency. I can see that the crystal and its parallel
adjustable capacitor are always in the circuit, but going to 1.0 switches out the
extra cap and switching to the 0.1 position adds some extra circuitry into the mix.
I don't quite understand how these other two settings do their job. If someone
could elaborate, I'd appreciate it.
IF deck tips                                     page 186

Date: Sun, 10 Apr 2005 12:57:08 -0700
From: "Dan Merz" <djmerz@3-cities.com>
Subject: RE: [R-390] 1.0 and 0.1 filter settings

Barry, the crystal may appear to always be in the circuit but it is bypassed by
C501 when the switch is in the 2,4,8,16 positions. The crystal filter is effective
only in the 1 and .1 positions. Apparently something is not adjusted correctly in
the crystal filter or the crystal is defective, which is causing the filter to reduce the
gain considerably. I don't recall messing with the crystal filter neutralizing in my
390a which is covered in the Y2K manual; others may have words of wisdom
about problems that arise in the crystal filter circuit, Dan.
Date: Mon, 11 Apr 2005 09:23:22 -0500
From: "Barry" <n4buq@aol.com>
Subject: Re: [R-390] 1.0 and 0.1 filter settings

Thanks for the reply. I see what you're talking about now. I didn't realize the
cap's job is to "bypass" the crystal, but okay on that. The problem seems to have
fixed itself somewhat. I'm in the process of recapping the IF deck. I'm replacing
a few caps at a time and testing between each "session" to make sure I haven't
toasted anything. If it stops working, I'll be able to narrow down where I may
have botched something. I replaced the two cathode bypass caps last night and
DeOxited the bandwidth switch contacts.

The last test seemed to be a lot better than the first one. The signal doesn't drop
nearly as much as before. I washed the deck thoroughly Saturday afternoon and
thought I had it dried out pretty good, but perhaps there was still a bit of
moisture hiding in critical places and that may have dried out better overnight.
Perhaps the cathode bypass caps in the first IF amp were leaky. Not sure what
improved it, but it appears to be working now. Six paper caps down in the IF
deck and nine more to go. I'm sure glad this is my hobby! Some of these are a
real pain to replace!
Date: Mon, 11 Apr 2005 11:33:14 -0400
From: "John KA1XC" <tetrode@comcast.net>
Subject: Re: [R-390] 1.0 and 0.1 filter settings

I'd recommend removing the cover from the L503 coil, and pull the 455 KC
crystal out of its socket and give the pins a cleaning and De-oxit treatment.
Date: Mon, 11 Apr 2005 21:13:35 EDT
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] 1.0 and 0.1 filter settings

OOPS, Have you pulled the cover off Z501 and observed that there is a crystal in
the location? Just one step in the trouble shooting process. The crystal is 455Khz
and they get garbed for other projects.
IF deck tips                                     page 187

Date: Tue, 12 Apr 2005 10:17:33 -0400
From: Roy Morgan <roy.morgan@nist.gov>
Subject: Re: [R-390] What is the difference between 390 and 390A

I can't remember the low IF frequency in the 180 - is it 60 kc?. I have an HQ-170A
on the bench right now. I'm reminded of the filters used in telephone/teletype
mulitplex systems since the 1930's. I have a couple of the filters used, one is at 80
kc I think (the ARC-5 low band receiver uses 80 kc IF, I think.) In any case,
finding such a band filter for the right frequency might well get you a voice band
width filter of superb performance. At the NRC publications-reprints page,
http://www.nrcdxas.org/ I find the following:

FILTERS. G. P. Nelson. Few commercial receivers covering the MW band have
adequate selectivity to cope with MW interference--particularly in the presence
of powerful local stations. Explains how to add mechanical filters to an existing
receiver for the ultimate in adjacent channel rejection. ( 21) "

"R31 THE SUPER HQ-180. Dallas Lankford. Add a Collins mechanical filter to
your "180". While not a "how-to" article, problems and results are discussed. (4)

"R43 CERAMIC FILTERS. Marc Bergman. A listing and description of the most
commonly available ceramic filters, with data from tests. (9) "

"R46 SURPLUS MECHANICAL FILTERS. Marc Bergman. Test results of several
reasonably-priced and available mechanical filters. (3) "

"R67 R390A KHZ FILTERS FOR THE HQ-180. Dallas Lankford. How to use
Collins DB filters in your HQ-180 receiver. (2) "
Date: Thu, 21 Apr 2005 19:32:55 -0400
From: Bob Camp <ham@cq.nu>
Subject: [R-390] DSP IF

The idea of putting a DSP IF processor on the IF output of an R390 sounds like an
interesting project. The nice thing about the 390 is that you can get at both the IF
output *and* the AGC chain without modifying the radio at all.

Given the high performance RF section and the mechanical filters the result
should be very competitive. Of course this gets into the general direction of
witchcraft and the like ....
IF deck tips                                     page 188

Date: Thu, 21 Apr 2005 20:01:46 -0400
From: "Dave Maples" <dsmaples@comcast.net>
Subject: [R-390] RE: DSP IF

All: It's not R-390, but is anyone aware of relative INEXPENSIVE DSP eval
boards still to be had? Everything I see now is $350-$400.

Trying to build an eval board is not on the possible list. I don't have (a) good
circuit layout software, (b) board-processing facilities, etc., etc., The idea of doing
I & Q demodulation for SSB really intrigues me...........
Date: Thu, 21 Apr 2005 19:15:39 -0500
From: "Cecil Acuff" <chacuff@cableone.net>
Subject: Re: [R-390] DSP IF

The thoughts of an 455 Khz IF based DSP filter system has been rolling around
in the back of my head for quite some time. An outboard accy. of that type
would be very popular considering the number of radios that use the 455 Khz IF.

I might try sending the IF output from my R-390A to the antenna port on my
Icom 756 Pro II and use the Pro as an IF/Processor/Demod and see how things
stack up... My understanding is that DSP processors that go up to 455 Khz are
quite expensive and mostly smoke and mirrors at this point. You'd have to
down convert to something lower....
Date: Thu, 21 Apr 2005 20:17:17 EDT
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] DSP IF

Can we do DSP in hollow state, Rack and room size are no problem but I do so
hate that sand state stuff even if I did slip a pair in for the 26Z5s?
Date: Thu, 21 Apr 2005 20:19:06 -0400
From: "John KA1XC" <tetrode@comcast.net>
Subject: Re: [R-390] RE: DSP IF

Dave, this isn't a board but it'll fit your budget. IK2CZL is a fellow R-390
enthusiast and has free PC DSP detector software. All you have to do is mix
down the 455 KC IF output down to anywhere between 13 and 18 KC and the
PC sound card takes care of the rest. I haven't tried it (yet) but it looks very cool
and would like to hear of anybody that has used it.
IF deck tips                                     page 189

Date: Thu, 21 Apr 2005 19:44:35 -0500
From: mikea <mikea@mikea.ath.cx>
Subject: Re: [R-390] DSP IF

Well, doing real DSP in hollow state will involve some hundreds or thousands of
tubes, with attendant heat, power, and reliability probs. It could be done, I
suppose, but you're talking about implementing a real computer in hollow state,
and that was found to be clunky and expensive. To do it _all_ in hollow state,
you'd end up using WIlliams-tube memory, instead of ferrite cores. Fun to
watch, but prone to screen burn-in, hard to keep aligned, and slow. Rack and
room size probably _would_ turn out to be a problem. So would air
conditioning. In dead of winter.
Date: Thu, 21 Apr 2005 21:50:56 -0400
From: "wjneill@lcc.net" <wjneill@lcc.net>
Subject: Re: [R-390] DSP IF

The original Army EINIAC artillery firing table computer was driven by a couple
thousand vacuum tubes and the TM for the sucker describes power
requirements, cooling requirements, and heat dissapation requirements that
were resolved only through industrial-strength solutions. And, the output of the
beast was directed to a Model 15 page printer in five-level 75wpm text.
Date: Thu, 21 Apr 2005 21:54:22 -0400
From: Bob Camp <ham@cq.nu>
Subject: Re: [R-390] DSP IF

The trade off is basically that with tubes you are better off doing the analog
processing. The digital stuff is just to hard to do. If you count up the transistors
the same thing is true with sand, but of course these days nobody counts
transistors. If you go with a 50 or 60 KC IF to feed the DSP stuff you could do the
conversion part with tubes ...
Date: Thu, 21 Apr 2005 22:26:56 -0400
From: "Michael Murphy" <mjmurphy45@comcast.net>
Subject: Re: [R-390] DSP IF

We built something like this at work (at a higher IF frequency 45 MHz!!). I'm no
expert but.. I think you have to sample the IF with an outboard A/D converter
first before sending it into the DSP to keep the costs down. If you want to talk
about a digital IF processor in an outboard box, the intermediate frequency
spectrum (of the R390A) is first digitized by an analog-to-digital converter (ADC)
into a slower digital data stream; this contains all of the signals present in the IF.
Nyquist says we need to sample at twice the frequency of our 455 kHz IF and
most converters can easily do this. Even low cost Sigma Delta converters (like
the one in your sound card) get close to being able to do this. There may be
some Sigma Deltas around which can do 1 MSPS or better.
IF deck tips                                     page 190

The digitized IF signals are then translated to baseband by something called a
Digital Drop Receiver or Digital Drop Converter (DDC). This could be a chip or
it more likely is code running in an FPGA or DSP core. Downconversion is
accomplished by digitally mixing the intermediate spectrum of frequencies with
a sinusoidal waveform generated by a synthesizer. The baseband output can be
thought of as the R390A receiver's 4th IF, which is selected from the DDC's other
output frequencies by a very efficient brick-wall digital filter. It is at this stage
that the outboard circuit can crank in some serious selectivity. Remember, we
are talking about programmable gate arrays or pure software in a DSP for all of
these stages and functions. The DDC's baseband output is fed to a DSP (or into
another section of the DSP or FPGA which is actually acting as a DSP), which
performs signal demodulation. The DSP's output is then converted from the
digital domain back into the analog domain by a digital-to-analog converter,
amplified, and is made available to Cecil via a bigass tube amplifier and a
Date: Thu, 21 Apr 2005 23:18:36 -0400
From: "Bill Levy" <levyfiles@att.net>
Subject: Re: [R-390] DSP IF

What a can of worms you have opened up. Why not just buy a DSP radio and
tune it to 455 and plug that into the 390A. Wouldn't that accomplish the same
darn thing. Now no one say why go to the expense of another radio......thats
what we do fellows. Any excuse to try something requires a new radio!
Date: Fri, 22 Apr 2005 09:29:02 +0200
From: "Bryce Ringwood" <BRingwoo@csir.co.za>
Subject: Re: [R-390] DSP IF

There's quite a few DSP sofware packages out there - one has already been
mentioned. Another on my computer is "Spectrum Lab". You'll need to convert
the IF down to 25kc/s with an MC 1496 chip (or similar, or better). - or a 7360 ;-)
I've got an old Analog Devices ADSP 2100 evaluation kit which I keep meaning
to play with, but never get around to it. How about simply putting a hollow-
state notch filter on the R390-A ? - that seems more "in-keeping with the
propriety of the radio".
From: "Tom Norris" <r390a@bellsouth.net>
To: "Bob Camp" <ham@cq.nu>
Cc: <R-390@mailman.qth.net>
Sent: Friday, April 22, 2005 10:44 AM

I have tried the IF out to my Pro II. Works well. Just put the 390/390A in 16KHz,
erm, I mean 16 KC bandwidth and connect the IF out to the Pro/ProII/ProIII
*receive input* (so you won't transmit into your 390!!) Works great! I have
considered taking the output directly from the final mixer before it goes to the IF
deck, but have been too lazy to try since it involves taking the top cover off,
which I can't do since the radio is in a rack (an open air rack, in case someone
IF deck tips                                     page 191

fusses) and I am especially too lazy to pull the radio, and my back, just to get a
few more KC of bandwidth.
Date: Fri, 22 Apr 2005 13:02:04 -0400
From: Bob Camp <ham@cq.nu>
Subject: Re: [R-390] DSP IF

I would like to try something that retains the mechanical filters. One thing you
could try is to do equalization in the DSP. That way you could take out the delay
and amplitude ripple of the filters in *your* radio. You could also turn the 16 KC
filter into something like an 18 KHz filter (a modern upgrade).

As long as you are matching things up you can also calibrate the AGC voltage.
More or less you build up a table of AGC versus db of attenuation. The R390 is
amazingly linear in this respect so it should work pretty well. The net result is a
"sort of" addition of more bits to your A/D converter. One of the reasons you
need as much of this kind of thing as you can get is that A/D converters are
relatively noisy gizmos. A 3 db noise figure converter is a tough part to find.

All of this would specifically match the DSP to the radio, but to me at least that's
an advantage rather than a disadvantage. If you had some memory on the DSP
you could store multiple radio profiles to match the various radios you used it
with. The calibration and equalization stuff is pretty much transparent in normal
use so you don't have a lot of added buttons or menus to cope with in normal
operation. The gizmo needs to be pretty user friendly if it's going to be of any
real use.
Date: Fri, 22 Apr 2005 13:14:59 -0400
From: Bob Camp <ham@cq.nu>
Subject: [R-390] DSP IF

Try 4. Keeps tripping the spam filter. If you go out and buy one of the black box
radios you still have the problem of what to do about the AGC feed back into
the R390. If you are after good AM you want to be able to cut back the gain on
the front end and IF's to keep everything linear. You can get 16 and 18 bit A/D
converters these days that will run up to the one or two mega sample range. To
do things right at 455KC it would be nice to be above a 2 MHz clock rate. In
order to get up to around 24 bits on the converter you are going to have to get
down to a 200 KHz clock. That would put your final IF at maybe 40 or 50 KHz.
Date: Fri, 22 Apr 2005 13:54:53 -0400
From: "Veenstra, Lester" <Lester.Veenstra@intelsatgeneral.com>
Subject: RE: [R-390] DSP IF

Suggest one of the usual DBF mixers and an LO of 465 will give the "audio
baseband" for the soundcard demod while the image will not be a concern
IF deck tips                                     page 192

Date: Fri, 22 Apr 2005 13:36:05 -0700 (MST)
From: Richard Loken <richardlo@admin.athabascau.ca>
Subject: Re: [R-390] DSP IF

My tastes are much more pedestrian, I want a synchronous detector so I can get
away from my daily doses of audio distortion brought about by fading issues
with the carrier and the sidebands. Always a way to consume time and money.
Date: Fri, 22 Apr 2005 13:42:45 -0700 (MST)
From: Richard Loken <richardlo@admin.athabascau.ca>
Subject: Re: [R-390] DSP IF

7 seconds with a 266 hmm? Now what would the delay be with the proposed
tube type DSP? Suppose we could build it out of TWT's to get the speed up.
How fast a digital processor can you build with a bunch of 12AX7's like IBM used
to implement the 701?
Date: Fri, 22 Apr 2005 23:25:04 +0100 (BST)
From: "Gary Bourgois" <flash@skybird.biz>
Subject: [R-390] IF out

A few years ago I took the IF out from my 390A and hooked it to the antenna
input of my SONY-2010, and tuned to a station with slop from an ajacent freq,
Turned up the Sony volume and flipped on the Synch detector, and low and
behold the interference was gone. The Sony audio does not match the great low
frequencies you can get from the detector output on the 390, and I have the one
with the probe jack on the front panel. Since my 390 quit a couple years ago the
bands have died. I have a lot of receivers, including a zenith console, and
everything is gone. Interesting that project HAARP made their own aroura
borealis a few months back. I live in the aroural zone, and radio has always been
weird. Now I can't get anything on the ham bands. Late nite talk show host Art
Bell (also a ham) has mentioned that there is something wrong with the
ionosphere, his band conditions are like mine. The only thing on shortwave is
EWTN, they cut through everything. Always have. WWCR is spotty.
Date: Fri, 22 Apr 2005 17:36:19 -0500
From: "Paul Staupe" <pstaupe@qwest.net>
Subject: Re: [R-390] IF out

Good discussion of the Sony 2010.... that used to be my quick way to get synch
detection out of the R-390. I'm lucky enough to have a Sherwood SE-3 that I use,
and now a nice MSR-9, (but it overloads.... any AGC experts out there?) Finally,
WEWN is my favorite.... I have been amazed in the past month though, they
have moved their former set in stone schedule to 5850 kc for most of the night
and well into the morning due to interference or propagation, I don't know
which.... I should call Glenn Tapley their SW director to find out....
IF deck tips                                     page 193

From: "Dave Maples" <dsmaples@comcast.net>
Subject: RE: [R-390] DSP IF

All: Absolutely good thoughts here. I'd be willing to fiddle with the DSP code if I
had an eval board for it, but it would have to compete with other projects. I've
had a DSP course in the past, and made As in it. It was really fun to get around a
new concept and wring it out..
Date: Fri, 22 Apr 2005 20:07:49 -0400
From: Bob Camp <ham@cq.nu>
Subject: Re: [R-390] DSP IF

What I'm after is AM that is easy to listen to. I'm not after Hi Fi, or AM stereo.
All I want to do it tune a station and listen to it with the least strain possible. The
SE-3 is a synchronous detector and it works very well with the R390. It certainly
works better than the other analog synchronous detectors I have used. That said
it isn't perfect. I think that with modern DSP and a bit of listening time (and
tweaking and listening) you can do better. Certainly with DSP you can "vote" the
sidebands by octaves. You can also do some stuff to null out heterodynes and
other junk. You are not going to get Hi FI audio (20 KHz 1 db point) out of an
R390 with a 16 KC filter in it. I also don't think that many of us have stations that
are clear channel enough to make something that wide practical.
 Date: Thu, 26 May 2005 16:01:08 EDT
From: DJED1@aol.com
Subject: [R-390] Dayton experience

<snip> I got a tour from Gary, who does all the restorations of "checked" radios.
He showed me the stash, which consists of about 5 pallets of blue stripers, and a
small number of parts chassis of the non-A.

Gary said he was having trouble finding good modules now, and will probably
run out of checked units in a year or so. LOTS of parts around, but definitely
needing repair. I think Fair does a lot of work (including painting the front
panel) on the checked radio for the extra couple of hundred they get.

The most interesting comment was that Gary has had some success with
rebuilding the mechanical filters. He finds that most have a broken wire in one
of the transducers, and he can repair or rewind the transducer and then replace
the filter in the housing using new foam. This may be necessary in the future as
the filters start to fail more frequently. <snip>
Date: Fri, 27 May 2005 09:52:53 -0700
From: "Dan Merz" <djmerz@3-cities.com>
Subject: RE: [R-390] Dayton experience

<snip> I picked up a BFO coil that I want to use in my external SSB adapter.
While Fair gave me the schematic for the current oscillator, I don't have any
IF deck tips                                     page 194

information on which of the three terminals is which. Can anyone identify
which of the terminals is the tap, which is the grid, and which is ground.<snip>

Ed, ok, I took a look at the BFO coil in the extra 390A IF chassis I have. If you
point the shaft end toward your eyes with the middle pin at 12 o'clock, the
terminals are numbered 1, 3, 2 in clockwise order with pin 1 at 11 o'clock, pin 3 at
12 o'clock and pin 2 at 1 o'clock. On my Artisan Electronics unit, the pins are
identified by a stamped number on the unit and these numbers correspond to
the schematic

Pin 1 goes to grid thru a capacitor
Pin 3 goes to ground
Pin 2 goes to cathode (center tap of bfo coil)

I checked the actual wiring on my unit in the chassis and the numbers stamped
on my unit indeed correspond as described. Hope this helps, best regards, Dan.
Date: Tue, 28 Jun 2005 12:43:59 -0500
From: "Dennis L. Wade" <DWADE@pacbell.net>
Subject: RE: [R-390] C-551 Replacement/AGC trouble?

The hot glue concept or similar is actually what I'm considering doing with the
new AGC capacitor. Lead length doesn't seem to be an issue since the two tubes
involved aren't even next to each other. I think just lifting the connections from
the old cap and attaching the new one to one wall will work out ok. From
looking at the AGC line, I think there may be some leakage somewhere as there
doesn't seem to be enough there. Any quick troubleshooting hints?
Date: Tue, 28 Jun 2005 14:16:53 -0400
From: Roy Morgan <roy.morgan@nist.gov>
Subject: RE: [R-390] C-551 Replacement/AGC trouble?

Put an ohmmeter capable of reading high resistances on the AGC line to ground
(notice if it reads the same with the nagative polarity on the line as with the
positive polarity on the line)..then unplug each module (RF, and IF) in turn to see
where you might be getting leakage. Knowing how the AGC wires run from the
source in the IF module to the rear panel terminal and the AGC switch and to the
RF module will help figure out where any excess leakage is. (One way to
measure low levels of leakage is to hook up a 9 volt battery to simulate AGC
voltage with a DMM on low voltage (or current) range in series plus side to
ground, negative to the AGC line.. You'll be able to detect microamperes of
leakage and normal AGC line currents. If the tubes are all cold, you may not
detect a leaky tube, but you will find any leaky caps or cable leakages. A
warmed up tube may leak more than if it's filament is cold.) THEN, with the
offending module connected, remove each of the tubes involved to see if you
have a leaky tube. If you find one, you are lucky. If you don't, remove the
module and find the (likely) leaky cap in there. Cable wires can be leaky, too, so
don't discount that possibility. Teflon wire in the AGC line would be a good idea.
IF deck tips                                     page 195

Date: Wed, 29 Jun 2005 11:00:59 -0400
From: "Tim Shoppa" <tshoppa@wmata.com>
Subject: [R-390] R-390(A) gain distribution

I grew up on 70's era QST's and ARRL handbooks with W7ZOI receivers. These
are extremely simplistic and generally don't have any more gain than needed.
What gain there is almost always comes after the mixer. (Except for maybe the
high bands where there'll be a RF amp on the front of the receiver). Obviously
the R-390/390A had a different set of critera and were working with differently-
capable components.

One criteria that I understand immediately is that you don't want any of the local
oscillators leaking back out to the antenna in a military setting. So the RF stage
before the first mixer is a necessity. It just so happens that there is plenty of
selectivity around it too. I'm just a few blocks from a powerhouse MW
broadcaster and I never have intermod problems in my R-390A! So even though
there is an active stage before the first mixer I've never had problem with IMD
there. This is one point where the W7ZOI designs have to deviate: the
transistors just never have nearly the dynamic range of a tube.

But 4 stages of 455kHz IF... why so much gain there? Most receivers of the era
had 2 (cheapie) or 3 stages and do just fine. How much gain is typically the 3-
mixer chain capable of? Each mixer gets fed from the AGC control line, right?

It's been a while since I looked at the Collins cost reduction report... is there any
thought given in there as to eliminating an IF stage?
Date: Wed, 29 Jun 2005 12:05:32 -0400
From: "James A. (Andy) Moorer" <jamminpower@earthlink.net>
Subject: Re: [R-390] R-390(A) gain distribution

You misunderstand what the IF stages in the R-390 series do. Don't forget that
the original
R-390 had 6 (!) stages of IF. Several of the IF stages have very low gain - no more
than 1 or 2. These stages provide additional selectivity - not additional gain.

In the R-390 and the R-392, there is even a stage with 3 (!) tank circuits, coupled
by 1 pf capacitors. You lose a lot of gain with low coupling like that, but you gain
in selectivity. The overall IF section needs to provide a gain of 1000 or so, but the
IF selection is almost entirely responsible for rejection of adjacent signals.

The Collins engineers needed to isolate the tank circuits from each other so they
would resonate independently and each contribute another 6 dB/octave of
rejection. If they are coupled too well, they stop acting as separate circuits and
behave as a single tank circuit.
IF deck tips                                     page 196

Date: Wed, 29 Jun 2005 14:51:02 -0600
From: "Kenneth" <crips01@msn.com>
Subject: [R-390] BFO question

I am going to get the BFO working on My R390A, once and for all. I have the
Y2K manual, of course, but I need a little advice. Here is what I have; the BFO
does not work, there is no calibration tone in the R390's audio but I can hear it
from the SBA-1 side band adapter, I can see a calibration carrier in the signal
strength meter on the R390. The tubes on the IF/RF module test good, if I can
trust my tube tester that is.

Where do I start on this to figure out what is going on. I have replaced the two
questionable caps in this module. The radio works fine otherwise. I have not
been too motivated to repair the BFO because of the side band adapter.
Date: Wed, 29 Jun 2005 19:22:37 -0400
From: "Jim Miller" <jmiller1706@cfl.rr.com>
Subject: Re: [R-390] BFO question

It is possible that the BFO knob could have been turned multiple times either
way putting the BFO frequency way off. It could be oscillating OK but be way
off frequency.
Date: Wed, 29 Jun 2005 23:22:42 -0400
From: "Jim Miller" <jmiller1706@cfl.rr.com>
Subject: Re: [R-390] BFO question

Mine doesn't have a center detent, but if I turn it on and turn the knob several
turns clockwise the beat tone will get higher and higher and then go away (it is
too farr off frequency), but I turn it back the other way several turns and I hear it
again. Just don't force it if it reaches the "stops" at either end. This may or may
not be your problem, just a thought I had. Could also be a bad contact on the
BFO switch.
Date: Wed, 29 Jun 2005 20:28:58 -0700
From: "Craig C. Heaton" <wd8kdg@worldnet.att.net>
Subject: RE: [R-390] BFO question

Chuck Ripple has a great description on IF Deck Alignment. The last thing to
do is the BFO, here is the link. http://www.r390a.com/html/if_deck.html
IF deck tips                                     page 197

Date: Thu, 30 Jun 2005 14:52:55 EDT
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] BFO question

Two of you were working on your BFO problems. It was suggested that you
loosen the shaft coupler between the deck and the front panel to back the knob
off the stop washer so the BFO could be adjusted from full end to end. The Idea
being your BFO was running fine and just way off 455.

One of you ask if the BFO had some kind of mechanical center. Sorry not so. The
coil will run from end to end and there is no "center" you just cranked the shaft
to move the coil from end to end. Once you found the 455 point, you set the
front panel knob and extension shaft up on zero. You adjust the knob, shaft, and
clamp to not cause undue friction and stop against the stop washer. The bushing
in the front panel has some play and can be adjusted to give a better center.
Loosening the green screws on the IF deck and moving the deck a bit may
improve the mechanical alignment of the BFO and band switch shafts.

If these simple checks did not get you in line, there are more things to do. Pull
the tube and run around the socket for voltage checks. Check that the BFO
on/off switch is turning the B+ on and off at the tube socket. Check your screen
and grid voltages. The filaments are good as they are in series with the PTO and
the receiver does play. Before you go for a coil can replacement, heat all the
solder joints. Cold solder joints are known to happen. The likely one are on the
pins of the coil can.

If this has not got you going the BFO coil can is known to fail. Back when you
just replaced them. Nothing actually went bad in the coil can that could not be
fixed.You can get the cans open and do an inspection and repair. Most problems
were in the form of cold solder joints or little broken wires. The coils have a
good range so fixes will not push them beyond the range where they will not
tune 455 plus and minus 3 as expected. The coil can is work to get it out and back
in. It can be done. I have done it a few times.

Let us know what you found your problems to be. Or if you got this far and still
need some more help. Roger KC6TRU
Date: Thu, 30 Jun 2005 18:41:00 -0700 (PDT)
From: Joe Foley <redmenaced@yahoo.com>
Subject: Re: [R-390] BFO question

<snip>...doesn't have a center detent... <snip>

If everything is assembled correctly this knob DOES have a center detent! But it
is inside the knob itself. If the knob is too far off the front panel the small
protrusion inside the skirt of the knob won't contact the stop. Pull the knob off
the shaft, you'll see what I mean.
IF deck tips                                     page 198

Date: Thu, 30 Jun 2005 23:28:42 -0600
From: "Kenneth Arthur Crips" <CRIPS01@MSN.COM>
Subject: Re: [R-390] BFO question

Thank for all of the advice. I would not have thought of the BFO shaft being
way out of position. What is interesting to me about this is this is the problem I
had with the BFO on the SP 600. It's stop pin was bent and let the shaft turn
freely. I am going to use my TS-510/U (HP-608C) RF signal generator to the
tweaking the IF module. Using to boatanchor piece of test equipment seems to
be the right thing to do. I need a manual for this beast does any one know
where I might download a copy.
Date: Fri, 1 Jul 2005 12:39:01 -0400 (EDT)
From: "William A Kulze" <wak9@cornell.edu>
Subject: Re: [R-390] BFO question

> BFO does not work, <snip>

Ken, the BFO on my unit didn't work when I got it. I could hear a very high freq
tone, but it didn't change when the knob was turned. The can had the label that
said don't open the can, but I figured hey, it doesn't work now, what the heck.
Turns out the slug had come loose from the shaft and was just sitting in the tube.
I glued it back in place and it was just fine after calibration. The chassis was bent
on one back corner, so I figured it was probably dropped. If this isn't the case
with yours, maybe it might help somebody else someday.
Date: Fri, 1 Jul 2005 16:37:20 -0700
From: "Dan Merz" <djmerz@3-cities.com>
Subject: [R-390] Hartley BFO FET Prod.Det.

Hi, I'm mostly thru the mechanical building part of the product detector for
390A similar to the one shown by AI2Q on this list, which has an AGC circuit in
addition to the detector/BFO, and just connects to the IF out, diode load, and
AGC connections on the back of the 390A. But instead of using the crystal-
controlled BFO oscillator I opted to use a tapped coil BFO unit in a can salvaged
from a National NC 100. In tapping the MPF102 FET BFO signal into the base
of the 2N2222 buffer stage, I wonder if it's best to take the signal from the drain,
much like an electron-coupled tube oscillator or from the source connection.
Most circuits I find for FET oscillators take the signal from the source, analogous
to cathode tap for a tube, and presumably a lower impedance coupling. Are
there any opinions on why most handbook circuits show the source connection?
I suppose either would work by fiddling with the various coupling impedances.
I've got a week of thinking about it before I'll be able to get back to the project.
Any thoughts? Best regards, Dan.
IF deck tips                                     page 199

Date: Fri, 1 Jul 2005 21:19:32 EDT
From: DJED1@aol.com
Subject: Re: [R-390] Hartley bfo FET Prod.Det.

Can't help you on the rational for where to tap off the RF, but the original
oscillator circuit I used had the oscillator output from the source, and the drain
was bypassed to ground at RF. So there was no choice as to where to tap off for
the RF.I'd be interested to know how you make out with your project- I
provided Alex with the original circuit which he published with some
modifications. I started with a variable BFO, and then last winter added the
crystal oscillator per Alex's circuit. I still think there has been nothing better for
SSB on the R-390A than this little SSB adapter, partly because it includes an
effective AVC, and partly because it requires no mods to the radio. Of course,
you have to be tolerant of mixing solid-state with our beloved tube radio.
Otherwise, a CV-157 is the right choice. I've taken some measurements of input
and output voltages which may be helpful if you have any problems. I've also
started working on adding a phase locked loop BFO so that the detector can be
used for synchronous AM. Not done yet though, waiting for winter.
Date: Fri, 1 Jul 2005 23:52:20 -0600
From: "Kenneth Arthur Crips" <CRIPS01@MSN.COM>
Subject: Re: [R-390] BFO question

I found a place that has originals for a very reasonable price. The problem is this
place uses Paypal for payment. I do not trust Paypal they have been hacked a
number of times. Fair Radio Sales has reproductions for 15 dollars I'll just get
one there. I am not really sure which 608 this one is, it's top voltage is 350 mill's I
understand this is how one tells these TS-520/U's apart.
Date: Sat, 2 Jul 2005 14:30:57 -0400
From: "Michael Murphy" <mjmurphy45@comcast.net>
Subject: Re: [R-390] Hartley bfo FET Prod.Det.

This is fun stuff. I have built them both ways as well. If you want the least
coupling and stability, (important if you are building a transmitter VFO and want
to key something upstream without chirping) I think the source connection is the
way to go.

For power, or if you want to multiply to a higher frequency, the drain is the way
to go. For raw p-p voltage, use this connection into your buffer. If you want
purity, the gate is the way to go. Actually, not the gate but the tuned circuit in
the gate. The tuned circuit itself can be coupled to, just like in the pre-ECO
Hartley days, with a good old link on the cold side of the coil. This gives you
some impedance flexibility too. It's a BFO; to hell with the buffer.
IF deck tips                                     page 200

Date: Sat, 09 Jul 2005 16:09:29 -0700
From: "Dennis L. Wade" <dwade@pacbell.net>
Subject: [R-390] AGC Troubleshooting

Got some time to look into the AGC trouble in my Motorola R-390A. First thing
I wanted to do is satisfy myself that there was indeed a problem. I looked at the
AGC line with a strong signal and the Calibrate sig. The most I could get was
about -4.9 volts at the AGC jumper. Under no signal conditions the AGC line is
about +0.15v. I then took the HP-410C and looked at resistance.

From the jumper to ground, I see about 350K to 400K with a strong capacitor
characteristic (i.e. much lower resistance rising as something charges).
Unplugging the RF deck doesn't change that, unplugging he IF deck I get a
steady 1.8 meg to ground from the jumper. I took out the IF deck and measured
resistance from pin 6 to ground, and I see about 7 meg with no charging
behavior. Looking at the Pearls of Wisdom, it says I should see infinite
Looking at the schematic I see the three capacitors AGC line to ground in the 1st,
2nd and 3rd if amps (C502, C512 and C519). These seem prime suspects to me.
Do you all agree, and any other components I should look at? I didn't take any
voltage measurements since the 7 pin extender socket I thought I had is actually
a 9 pin. :/.
Date: Sun, 10 Jul 2005 00:04:34 EDT
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] AGC Troubleshooting

I took out the IF deck and measured resistance from pin 6 to ground, and I see
about 7 meg with no charging behavior. it says I should see infinite resistance. If
you were doing this in 1970 with a TS 505 or a TS 352 on the K ohm range, 7 meg
would be infinite resistance. You are likely OK on this test. TM 11-5820-358-35 8
Dec 1961 Para 72 b. Alignment of Z503 Page 113. says AGC should be in the
range of -1 to -2 volts My mail only goes back 5 days, so I do not have your
original problem with your AGC. Watch the other responses and keep asking
questions until you feel you and your receiver are happy.
Date: Sat, 09 Jul 2005 21:48:45 -0700
From: "Dennis L. Wade" <dwade@pacbell.net>
Subject: Re: [R-390] AGC Troubleshooting

Thanks for the reply Roger. Good point. 7 meg may not indeed be a problem.
But why don't I see the 350K I saw from the AGC jumper? So let me review why
think there is a problem:

1. With all modules connected, from the AGC jumper to ground is about 350K.
When the RF deck is disconnected, it remains the same. When the IF module is
disconnected, it goes to about 1.8M to ground. Does this isolate it to the IF deck?
IF deck tips                                     page 201

2. I don't see more than about -4.9 vdc at the AGC jumper on very strong, or
the cal, signals. No signal is +0.15

3. There is distortion on strong signals.

Note that I have not re aligned the receiver yet, I still have some caps to replace
in the AF deck. I'd like work on the IF deck if I need to while I have it out.

Two basic questions: Do I have an AGC problem given the measurements
above? And, is it isolated to the IF deck?
Date: Wed, 13 Jul 2005 17:24:46 -0500
From: "Dennis L. Wade" <DWADE@pacbell.net>
Subject: [R-390] More AGC Questions

In attempting to keep my sanity, I've been looking further at the IF deck I have
on the bench to figure out why I might have low AC. I discovered that my A-OK
filter is dead. Could this drag the AC line down? If it did, wouldn't I see that on
an ohmmeter test? The AC line in the deck doesn't show excessive leakage to
ground however. This deck is frustrating me because its not behaving like it has
a problem in terms of the resistance checks I've done.
Date: Thu, 14 Jul 2005 00:52:53 EDT
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] AGC Problems

If switching over to AGC is not just plain killing the signals or you cannot tell the
difference between AGC and MGC modes, you are likely OK. You only have
one receiver (yours) to listen to. If you were an O5H, 33B, 31E, or any other MOS
that used the receivers and had a chance to listen to several hundred receivers,
you would know when you were listening to a bad one. So your AGC questions
are a wise pondering. A full review of the subject starting from some recent post
follows. Remember first that in the MGC position, the AGC line is simply
shorted to ground in the function switch. The line at ground in MGC pulls the
grids of the AGC controlled tubes toward zero volts. Cathode resistors in the
tube stages provide some positive cathode voltage relative to the grid voltages.
AGC voltage is negative. When the AGC voltage is applied to the grids of the
tubes, it drives the tube stages toward cutoff. A couple volts on the grid of a tube
that is working on micro volt signals go a long way in signal reduction.

If you have no signals in either the AGC or MGC mode, you expect you have a
tube stage problem and have no reason to expect it to be related to the AGC line.
You trouble shoot to find the stage that is not making the grade. The found
problem may be in the AGC line, but it will not be the symptom that leads to a
logical troubleshooting progression.

If you have an AGC voltage in the MGC mode, you should check the wire
harness and function switch. In MGC mode the AGC line is not being held to
IF deck tips                          page 202

ground by the function switch.If you have strong signals in the MGC mode you
may have just one more bad item pulling the AGC line to ground. No Problem.

When you switch on the AGC you expect the negative AGC voltage to reduce
the receiver gain a little bit. If you get no AGC gain reduction then you have to
wonder if the AGC line is shorted somewhere and the receiver acts as if it is still
in the MGC mode.

The carrier level adjust has been a sorry circuit since the day it was implemented.
Unless you have changed some of the parts, to improve the performance, what
ever your carrier meter shows you when switching the AGC is not a real
inspirational troubleshooting step.

You likely expect you have an AGC problem when you switch to AGC and you
loose all your signals. Or a lot of the signals. How does opening a line from
ground, and placing almost no negative voltage on it cause a loss of so much
receiver gain?

You likely expect you have an AGC problem when the receiver starts acting
intermittent with gain coming and going. The receiver appears OK in the MGC
mode but looses signals in the AGC mode.

Now you are not looking for a shorted item. A shorted item in the AGC line
looks like MGC.

You are not looking for an open resistor. The resistors work fine in the MGC

>Barry - N4BUQ wrote, "When listening to a moderately strong station in the
>15mc band, if I switch to AGC, the signal drops significantly from the MGC
>position, regardless of the AGC speed."

This may not be bad. If the signal in the MGC position is strong, the receiver is
being over driven and when the AGC is switched on, the strong signal produces
an AGC voltage and a resulting signal level that is smaller than the MGC level
but not over driven or distorted. However, if the receiver seems to loose lots of
signals in the AGC mode, there is a problem. If the IF gain is not set to high (-7
volts) and the receiver loses it in AGC expect a problem.
A most common AGC problem is with the mechanical filters. The AGC line
crosses R507 (22K) and is filtered by C512 (5,000pf). From there the AGC voltage
is applied through all four filters, all the time. If one filter is pulling the AGC
voltage to ground this is a problem. The filters may appear to have good band
pass and performance so a simple check of bandwidth and sensitive with a signal
generator and meter on the diode load may not find the filter problem.
However this is a good first test if you have a signal generator. 200- 250 UV at
455Khz into the IF deck and rock the generator both sides of center to find the
bandwidth of each filter. Note the diode load voltage for each filter and see if one
of them has more loss than the others or has a very wide response.
IF deck tips                            page 203

The next step is too place a tube extender under V502. You want to look at the
control grid voltage. The AGC is applied to the control grid through the selected
filter. As the AGC is applied to all filters, and if a filter is sucking AGC, the "bad"
filter will pull the AGC all the time. If you have a bad filter, you would expect
zero volts on the grid, as opposed to several volts negative. The TM shows the
grid to only be 0.4 volts negative. So this test is not a real sure bet either.

Ohmmeter checks may not get you anywhere either. On one side all four filters
are tied to the AGC line. If the short were near that end of a filter coil winding in
one filter, all four filters would read the same meter value. Thus you have no
clue which filter is bad.

Good trouble shooting practice never supported unsoldering wires just to see
what will happen. Heating mechanical filter terminals is not a high item on things
I would do this week.

But, if we open R507 and remove all AGC from the stage. Pull the AGC wire
from the resistor and let that wire hang open. Short the end of R507 to ground,
so the stage thinks it has zero volts AGC. Now review your AGC and MGC
operation and retest the filter band pass with the signal generator and see how
the receiver behaves. Missing AGC on one stage should give about normal
performance. If all of this work has not isolated one of the filters as a candidate
for concern, I would give them a passing grade and go on to the next likely
Second most likely AGC problem after the filters is the bypass caps on the AGC
line. Locate the green screw extractor, Bristol wrench, schematic and meter.
Go down the AGC line and just meter every cap and resistor.
>Barry N4BUQ wrote, "With a signal generator as input and the RF gain all the
>way CW, I can adjust the signal generator to get -10V on the Diode Load in
>MGC. Switching to AGC, the Diode Load drops to about 3.4V to 4V (depending
>on the AGC speed position)."

This is not a problem, -10 volts on the diode load is over driven by 3 volts. This
should produce lots of AGC. The balance point is where going from AGC to
MGC to AGC produces no change on the diode load. This may not be -7 volts.
This may also not be the optimum operating point for the IF gain adjustment
setting. So we never consider what this balance voltage point may be.
>Roy Morgan offered the following to help deal with leaking caps on the AGC
>line: Put an ohmmeter capable of reading high resistance on the AGC line to
>ground (notice if it reads the same with the negative polarity on the line as with
>the positive polarity on the line). Then unplug each module (RF, and IF) in turn
>to see where you might be getting leakage. Knowing how the AGC wires run
>from the source in the IF module to the rear panel terminal and the AGC switch
>and to the RF module will help figure out where any excess leakage is.
IF deck tips                                  page 204

Pull the AGC jumper off the back panel and hang an amp meter across the
terminals. Observe the correct negative voltage polarity. You'll be able to detect
microamperes of leakage and normal AGC line currents. Most DMM and analog
meters have low amperage ranges that will handle the AGC current range. We
do not know the current of a good AGC line so until someone makes some test
and offers some values the number your meter produces is not going to help.
Will someone please make a test of AGC current and offer up the values they
get? Inquiring minds want to know.
>Roy Morgan offered (One way to measure low levels of leakage is to hook up a
>9 volt battery to simulate AGC voltage with a DMM on low voltage (or current)
>range in series plus side to ground, negative to the AGC line. You'll be able to
>detect microamperes of leakage and normal AGC line currents. Start with a
>cold receiver. If the tubes are all cold, you may not detect a leaky tube, but you
>will find any leaky caps or cable leakage. Cable wires can be leaky, too, so don't
>discount that possibility. Teflon wire in the AGC line would be a good idea. Roy
>Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!

Then turn the receiver on. A warmed up tube may leak more than if it's filament
is cold.) If the problem is in the RF deck and you use a battery, unplugging a RF
deck that is good should produce little change in current. The AGC stages are all
in the IF deck. Unplugging that deck opens so many AGC lines coming and
going you have no idea which end of the circuit is being offensive. This is the real
problem of trouble shooting the AGC line in the receiver. Remove each of the
tubes involved to see if you have a leaky tube. If you find one, you are lucky. If
you don't, remove the module and find the (likely) leaky cap in there.
>Dennis wrote, "Good afternoon, got some time to look into the AGC trouble in
>my Motorola R-390A. First thing I wanted to do is satisfy myself that there was
>indeed a problem. I looked at the AGC line with a strong signal and the
>Calibrate sig. The most I could get was about -4.9 volts at the AGC jumper.
>Under no signal conditions the AGC line is about +0.15 "

OK, these are not bad numbers. Once the -4.9 volts get back to several tube grids
it is on the order of less than -1 volt. At no signal we expect no AGC and a value
of .15 plus is typical.
Dennis, I took out the IF deck and measured resistance from pin 6 to ground,
and I see about 7 meg with no charging behavior. It says I should see infinite
If you were doing this in 1970 with a TS 505 or a TS 352 on the K ohm range, 7
meg would be infinite resistance. You are likely OK on this test. TM 11-5820-358-
35 8 Dec 1961 Para 72 b. Alignment of Z503 Page 113. says AGC should be in the
range of -1 to -2 volts
Thanks for the reply Roger. Good point. 7 meg may not indeed be a problem.
But why don't I see the 350K I saw from the AGC jumper? So let me review why
think there is a problem: 1. With all modules connected, from the AGC jumper to
IF deck tips                             page 205

ground is about 350K. When the RF deck is disconnected, it remains the same.
When the IF module is disconnected, it goes to about 1.8M to ground. Does this
isolate it to the IF deck?
No not really. When you unplug the IF deck you open so many wires in the
AGC line coming and going from the rear panel, front panel function switch,
from the AGC diode, to AGC controlled stage, you just never know what you
are checking. If you do not have a good schematic in front of you and consider
what you have disconnected at any give instance of measurement, you can run
your self ragged.
I don't see more than about -4.9 vdc at the AGC jumper on very strong, or the
cal, signals.


No signal is +0.15


There is distortion on strong signals.

OK. R390/A are known for this aspect.

Two basic questions:
Do I have an AGC problem given the measurements above?
 And, is it isolated to the IF deck? Dennis
So we come full circle to your original question. The part not really dealt with
here is, If the AGC is killing lots of signals and is related to one of the mechanical
filters, how do we determine good and bad filters.
First I will go read the archives and see what I find. I'll kick out a new post when
I get there. Give me a few days to read up.
Dennis, I would say you are likely OK with your receiver. Go on with your other
roubleshooting and cleaning. If you do have an AGC problem, operating the
receiver will not cause more damage. You can always operate in MGC if you
think you may have troubles with the AGC. You can always come back to the
problem if it is still nagging at you. Having one receiver in isolation to care for
by your self is a daunting task. The military trained us guys in groups to take
care of bunches of receivers together with support, and this scared the hell out of
most of us. Most of the tecks never got confortable about being repairmen. They
did one four year enlistment and got out of the trade altogether. It was just not
the military they did not like. They gave up electronics in general. Being a fellow
willing to work on a glowing receiver puts you in a special class. Just being
willing to give it a go earns you respect. Do not worry that you are working
from a disadvantage. You have to start somewhere and you are down the road
IF deck tips                                     page 206

of glowing tubes. Just because some of us ran ahead and come back with tales
does not make us any better. Do not let our tales worry you.

Roy Morgan added his best thoughts. Barry put in with his findings. No one has
taken us to task for being way off base on this, so we are likely in the park.
Date: Wed, 13 Jul 2005 21:58:41 -0700
From: "Dennis L. Wade" <dwade@pacbell.net>
Subject: [R-390] Re: More AGC Questions

Thanks for the responses. Some have asked what the problem was, so I'll recap
my previous post. By the way, it's the 16 Kc filter that's dead, not the A-OK
:(AGC voltage on most over the air signals is around -4-5 vdc No signal voltage
is about +0.15 Very strong/close BCB station generates about -10, pins the
needle, and distorts.

Question 1. I do have a problem, right? Resistance from AGC jumper to ground
350K with a capacitor charge behavior. Unplugging the RF deck does not change
it. Unplugging the IF deck puts the jumper at 1.8 meg to ground.

Question 2. Does this isolate the problem to the IF deck? Thinking that it does, I
figured I'd see the same 350K or less to ground from pin 6 (AGC line) of the IF
deck connector to ground. But no, its about 7 meg. This is what's confusing me. I
just received my 7 pin test sockets, so if this heat ever lets up, I can take more
voltage/resistance readings from V501 502 and 503. Note that I have not
realigned the radio yet, I've recapped the RF deck and am working on the IF
deck. I was hoping to solve this ACG problem before going in for a full
alignment. Please excuse the repletion for those who saw the previous posts.
Thanks for the help. Sign me Frustrated in Carmichael, Dennis
Date: Thu, 14 Jul 2005 08:09:06 -0400
From: JMILLER1706@cfl.rr.com
Subject: Re: [R-390] AGC Problems

There is supposed to be a jumper on the rear panel termial strip for a remote
AGC line? What would happen if it was missing?
Date: Thu, 14 Jul 2005 19:05:45 EDT
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] AGC Questions

If you have a 16K filter bad, the side effect could be a bad AGC. The output of all
the filters is tied together on one side to the AGC line. The other side of the filter
outputs are switched through the band switch. The unused filters are shorted
when not in use. A known side problem with bad filters is the AGC acts funny.
This depends on exactly what goes wrong in a given filter. You can have a bad
filter without having an AGC problem. Ignore the bad filter and AGC problems
for a while and work on the other items you have on the list of thing you want
to do. You could open the lines to the bad filter and just let it hang. See if this
IF deck tips                                     page 207

changes the AGC behavior. Then every thing but the that IF band width would
work for you. And you can get to the filter replacement whenever you feel the
Date: Thu, 14 Jul 2005 19:22:56 EDT
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] AGC Problems

>..supposed to be a jumper on the rear panel termial strip for a remote AGC ....

In the R390/A, V201 the RF amp has a R234 a 1.5 meg resistor on the AGC line
to ground. So with no jumper this resistor completes the circuit path for the AGC
line on the tubes that have AGC on the control grid. In MGC where the AGC line
is shorted, there are other resistors in the AGC line between the grids and the
short point on the function switch. There will be a small loss of receiver gain in
MGC with the jumper missing. You likely may not even be able to hear the
difference between jumper and no jumper with the function switch set to MGC.
In AGC, no AGC voltage is fed back to anything, The AGC and MGC positions
on the function switch will act exactly alike to you. The carrier meter will peg
over when switching AGC time constants because all that circuit is before the
back panel jumper. The audio will not be lost like normal however when
changing the AGC time constant, because the AGC charging time, when
switched, is not being carried over the jumper and applied to the tubes. If you
did not know, you could run the receiver for years with the AGC jumper
missing and never miss a thing. As much as the receivers AGC performance has
been cried about, you may think your receiver is just normal.
Date: Fri, 15 Jul 2005 23:51:23 EDT
From: RIKKA3TXR@aol.com
Subject: [R-390] Re: C553

My '56 r-380a had a brownie in the C553 position..I still have all the pulls in a
bag..But never checked them for leakage...It's not a question, I just replaced
it..Not worth the money for new filters........ <snip>
Date: Sat, 16 Jul 2005 13:24:00 -0700
From: "Dennis L. Wade" <dwade@pacbell.net>
Subject: [R-390] AGC Problem Fixed :))

The nagging not-quite-right AGC line in my Motorola '390A has been fixed. The
culprit: V509. Got out to the garage early enough to avoid the heat and took
some voltage readings on the signal grids of V501, 502 and 503. All were slightly
*positive* under no signal conditions. Pin 2 of V509 was also slightly positive. In
my research through the Pearls (many, many thanks Wei Li), I kept seeing posts
from Dr. Jerry that said in essence...positive grids are either from leaky caps or
gassy tubes. I wasn't finding any strong evidence of leaky caps. So, almost on a
lark, I swapped V506 and V509. Voila!! Negative grids return. Hooked up an
antenna...noticeable improvement in audio quality. The offending tube does not
test gassy on my emission type tester however, although that doesn't surprise
IF deck tips                                     page 208

me. So, Roger, your advice was sound..that is...go on with it and finish the radio.
And I was...but after just oneeeeeee more thing to try. Thank you all for your
help. I'm sure you'll hear from me again shortly as I continue on. :)
Date: Sun, 17 Jul 2005 15:08:42 -0400
From: shoppa_r390a@trailing-edge.com (Tim Shoppa)
Subject: [R-390] Excessive backlash in BFO pitch control

One of my IF decks has excessive backlash in the BFO pitch control. e.g. if I'm
turning to the right, it zero beats at "0", but if I'm turning to the left, the zero beat
is closer to "+1". Mechanically, I see an accordion-type coupling between the shaft
and the reactor. Is this where I should be concentrating my effort, or should I be
looking inside the variable inductor itself? Alignment between all the shafts is
less than peachy, too. But I cannot see how this would give more than a tiny bit
of backlash.
Date: Mon, 18 Jul 2005 12:37:53 -0500
From: Tom Norris <r390a@bellsouth.net>
Subject: Re: [R-390] Excessive backlash in BFO pitch control

Try loosening the bushings both at the IF deck and the front panel to make sure
there isn't any binding, then take a good look at that coupling and make sure the
setscrews are tightened and there are no cracks in the body of the coupling. A
crack or break can cause the shaft to turn fine one way, but not so fine the other.
Date: Sun, 24 Jul 2005 07:37:05 -0400
From: "Bill Coleman N2BC" <n2bc@stny.rr.com>
Subject: [R-390] R390A AGC
         My R390A has an AGC problem. With no signal the AGC voltage is -0.5V
(measured with an HP410C VTVM). The AGC responds properly to signals
(goes more negative to a max of appx. -15V). Resistance measurements on the
AGC line look OK:

IF strip @ J512-6 = Infinity     AGC line @ J512-4 = 482K RF deck @ J108 =
With P512 and P108 in place, the AGC jumper on the rear = 378K

The only other voltage that is wrong is the IF strip suppressor grid bus,
measures +3.4V should be -2.5V I suspected Z503, I couldn't get it to peak -
Output increased as I cranked out on the slug but it ran out of adjustment range
before peaking. Just replaced Z503 (nasty) and have the same result. I've gone
thru 3 wholesale changes of tubes in the IF deck. I've replaced C545, C546, C548.
(I keep coming back to the AGC IF Amp area) Ideas?
IF deck tips                                     page 209

Date: Sun, 24 Jul 2005 08:43:10 -0400
From: "Bill Coleman N2BC" <n2bc@stny.rr.com>
Subject: Fw: [R-390] R390A AGC

Thanks Don, I should have put more info in my original post.... I have 'lifted'
the AGC line at each stage of the IF one at a time (disconnecting the appropriate
isolation R), the AGC voltage and the suppressor grid bus does not change.
Also, measurements in the IF with the RF deck disconnected are unchanged. I
did the 9V battery trick too. Readings at each of the stages are appropriate.
That's why I keep coming back to the AGC IF AMP, Rectifier and Time Constant
 stages. Z503 will not peak, all other stages peak nicely. It seems that the gain of
the AGC IF amp is low because Z503 will not peak. I suspect the reduced output
is not enough to overcome the positive bias coming from the R544/R546/R545
divider string (roughly +17V if I did my Ohms law correctly).
Date: Tue, 26 Jul 2005 15:46:06 -0400
From: "Bill Coleman N2BC" <n2bc@stny.rr.com>
Subject: [R-390] R390A AGC troubles

Maybe my earlier posts were lost in the fan / audiophile / Depot Dawg
discussions. Observations:

1) Low AGC voltage (zero signal = -0.5V)
2) Suppressor grid bus (V504 & V508) is +3.4V, should be -2.5V)
3) Z503 will not peak before it's slug "tops out" in the core

I have isolated the decks, measured everything that is measurable, replaced caps.
I have isolated individual IF stages and swapped tubes. All without making
progress. The more I poke, measure and isolate, the more I am convinced that
the problem is in the AGC Amp stage(s) rather than out on the AGC bus. All
resistance measurements along the AGC bus are OK, voltage measurements
when fed with a separate source (9V battery) are OK. Along the way I managed
to destroy Z503 so I pulled one out of a 'cadaver' IF strip. I noted that it's slug is
fairly well centered in the core. Upon replacing Z503, the 'new' one behaved the
same way.... increasing stage output as the slug was cranked toward the top but
it runs out of adjustment before peaking. I fed the AGC Amp stage directly with
my siggen at 450kc and Z503 will peak with the slug slightly further down in the
core. I have snugged all the ground points in the entire IF chassis & replaced
everything in the V508 stage except the tube socket. I think I'll disassemble the
gear train, polish the parts and reassemble blindfolded, that will be less
frustrating! Ideas greatly appreciated 73, Bill N2BC                                     PS: I have no
fan installed, use a plain highly oxygenated line cord, and the receiver's mixed
Stewart Warner / Collins / EAC heritage is usually just a lovable as my
Lab/?/Shepard best friend.
IF deck tips                                     page 210

Date: Tue, 26 Jul 2005 15:53:40 -0400
From: "Jim Miller" <jmiller1706@cfl.rr.com>
Subject: Re: [R-390] R390A AGC troubles

My old S&W had AGC problems which seemed to be centered around Z503. I
remember having to work with it to eliminate a short to ground between one of
its pins and the chassis. Seemed the chassis cut out for the transformer needed
enlarging a bit. Another oddity that happened in the same radio was a
breakdown in the center insulation of the small shielded cable carrying the diode
load signal...would cause popping and loss of AGC..this doesn't seem to be your
case however.
Date: Tue, 26 Jul 2005 15:54:58 EDT
From: Llgpt@aol.com
Subject: Re: [R-390] R390A AGC troubles

It is quite possible the "cadaver" Z-503 is a bad one too. They are a known
troublesome part. If possible try a known good IF deck. Maybe you have a
friend close by.
Date: Wed, 27 Jul 2005 10:05:33 -0400
From: Gord Hayward <ghayward@uoguelph.ca>
Subject: [R-390] Re: Z503

Mine had a similar problem and unfortunately I killed the coil when I tried to fix
it. The winding is potted in goo (not ukumpucky) and the ferrite is on the
outside of the coil too. When I tried to get the coil apart with heat I really did it
in. So, I took a honking big coil from my junk box and a small cap and rebuilt it.
It peaks and the set performs at spec now. The trick was to use a big coil to get a
high enough Q which determines the impedance of the parallel resonator and
hence the stage gain at resonance. (big L, small C = big Q)
Date: Wed, 27 Jul 2005 14:30:34 -0400
From: Gord Hayward <ghayward@uoguelph.ca>
Subject: [R-390] Re: Z503

It should resonate at 455 kHz. The coil I used looked like one of the old loopstick
variable coils for crystal radios. I think the capacitor was somewhere near 30 pF.
I stuck it together and peaked it with a scope and signal generator to be sure it
would work before I started the surgery on the 390A. I removed the can top,
pulled out the old coil and cap, put in the new coil and cap and replaced the can
top. The result looks like it was meant to be there. Then I repeaked it in the
radio as in the standard alignment instructions. Remember, the Q is quite
important. I did try a smaller coil that also peaked, but the Q was too low so I
didn't get enough AGC action.
IF deck tips                                     page 211

Date: Wed, 27 Jul 2005 15:11:42 -0700
From: Dennis Wade <sacramento.cyclist@gmail.com>
Subject: Re: [R-390] R390A AGC troubles

I'm at work, but I don't recall that -0.5V zero signal on the AGC bus was a
problem. When I finally got mine fixed (different problem though, see previous
posts) the small + zero signal voltage I had been seeing became -0.4V. What are
the grids of V%01, 502 and 503 doing? What do you "hear" in terms of
symtoms..how does the radio sound under various signal conditions?
Date: Wed, 27 Jul 2005 18:31:33 -0400
From: "Bill Coleman N2BC" <n2bc@stny.rr.com>
Subject: Re: [R-390] R390A AGC troubles

Hi Dennis, it was my understanding that zero input signal state is around -7V.
The other measurement that is 'wrong' is the suppressor grid voltage on V504 &
V508), it is +3.4V, should be -2.5V. The voltage on the grids of the IF strip is
consistent with the -0.5V. Externally, it sounds like minor overloading on strong
Date: Wed, 27 Jul 2005 21:13:55 -0400
From: "Jim Miller" <jmiller1706@cfl.rr.com>
Subject: Re: [R-390] R390A AGC troubles

Another thought: The antenna trimmer control shaft and gears are at AGC
potential in the RF stage. The phenolic gears and washers insulate the shaft from
ground. If someone over-lubricated the antenna trim gears, the lubrication oil
could be forming a path to ground and shunting the AGC in the RF stage, which
could create overload or poor AGC action. The shaft and gears need to be
purged with a chemical cleaner like Big Bath to rid them of any oil.
Date: Sun, 14 Aug 2005 19:16:47 -0500
From: Tom Norris <r390a@bellsouth.net>
Subject: [R-390] Differences in 390A IF decks

The tech manuals mention differences between older and newer 390A IF decks,
and folks here have, in the past, brought up that older Collins decks were
different. Indeed they are. If anyone wants to add an additional photo to their
390A photo collections, below is a link to assorted detail photos just shot of an
unmodded early Collins IF deck. No dates could be found anywhere.
http://www.fernblatt.net/forradio/R390A/; Just click on the files that start with
collins_r390a_IF..... etc There are a few shots of a fairly late Collins 390A in there
as well. I've only come across a couple of Real Live Collins 390A's, plenty of the
radios made by other contractors. Feel free to use any photo you wish, and
anything else in you find stored on my server. If you click on "parent directory"
then go down a bit, there are loads of other images including a directory full of
photos of Fair Radio's old place. The Collins 390A shown in the pics? It's been
gone for a year, sorry guys.
IF deck tips                                     page 212

Date: Mon, 15 Aug 2005 05:43:52 -0400
From: shoppa_r390a@trailing-edge.com (Tim Shoppa)
Subject: Re: [R-390] Differences in 390A IF decks

I assume you're talking about the fixed rather than variable caps around the
filters? I have an IF deck that is Motorola and has the fixed caps too. Not sure if
it was originally that way from the factory or was a result of parts-swapping at
the depot, but I was always under the impression that many Motorola IF decks
lacked the variable caps and the chassis holes. What exactly is that doo-dad in the
ballast tube socket?
Date: Mon, 15 Aug 2005 08:43:27 -0500
From: Tom Norris <r390a@bellsouth.net>
Subject: Re: [R-390] Differences in 390A IF decks

Tim, you know that, and I know that. I had posted the links for the benefit of
those that didn't or for those that collect photos for no good reason. Or for good
reason, either one. I think there is at least one, who I forget, that likes new and
different pix taken.

>...about the fixed rather than variable caps...................

yup, and the fact it's a Collins [Blessed be Art, etc] AFAIR all the Motorola and
Collins decks pre 1954 had fixed caps. I suppose most Mot/Col decks out there
will be capless, since they weren't made past '56. An odd thing about the deck in
the photo - there is no contract number marked anywhere on the thing. Just a
Collins p/n and a serial. The other Collins 390A's I've had had the contract
numbers, at least I think so. I may have been hallucinating at the time, though.
heehee Tom M reminded me of the different sheet metal design and other
things that were used in later contracts by EAC. I may also do comparison pix
showing those as well, I probably have an extra EAC module around here
somewhere. (rummage rummage)

>...........doo-dad in the ballast tube socket?................

The doo-dad? It's a "Modified Horizontal Low Resistance Current Pass Device"
Which means I have a 9-pin shorting plug underneath instead of a b*11*st. The
tube shield and label are there for effect, since the radio is going out the door to
someone with an odd sense of humor. I used 12BA6's for PTO and BFO. The
radio is an Amelco, but it's a mutt. While it has an Amelco RF deck and P/S, the
IF is Collins and the audio is Stewart-Warner. Now if the p/s were Helena-
Rubenstein, we'd be all set.... hehe
IF deck tips                                     page 213

Date: Mon, 15 Aug 2005 05:38:23 -0700 (PDT)
From: "Tom M." <courir26@yahoo.com>
Subject: [R-390] EAC and Differences in 390A IF decks

EAC pioneered a new assembly procedure to assemble IF decks and others (RF I
think) "in the open" and then fold up the sheet metal. They got permission from
Ft. Mom to do this. Notice how late EAC decks have different sheet metal folds
than others. EAC also got special permission to make wire splices to enable this. I
got this info from Robert Edwards of EAC. Interestingly enough, the Fowler IF
decks were made the original "Collins" way. The EAC mods did not stick to the
drawings issued to Fowler. Everyone confused yet?
Date: Mon, 15 Aug 2005 15:09:58 -0400
From: "John Bunting" <john@gumlog.net>
Subject: Re: [R-390] Differences in 390A IF decks

Motorola's Order No. 14-PH-56 was the first order that required the order
number and the serial number to appear on all modules. Partway through that
order the three fuse modification was made too.
Date: Mon, 15 Aug 2005 14:25:28 -0500
From: Tom Norris <r390a@bellsouth.net>
Subject: Re: [R-390] Differences in 390A IF decks

Thanks John. I was aware of the fuse mod, but not the order number and S/N
information. Must have just overlooked it.
Date: Sun, 21 Aug 2005 17:07:40 -0400
From: Mark Huss <mhuss1@bellatlantic.net>
Subject: Re: [R-390] R-725

Basically an R-725 is an R-390A modified for HF DF using an array of vertical
antennas and measuring the phase delay of the wavefront. Because of the phase
shift in the mechanical filter across its response curve, they substituted an R-390
IF deck for the R-390A IF deck, then added a whole s***pot full of ferrite beads to
suppress leakage normally present in the R-390A. the result is the quietest and
most sensitive R-390A made. In the shop I worked in, they always had at least
6dBm better signal to noise ratio.
Date: Sun, 21 Aug 2005 16:14:25 -0700 (PDT)
From: "Tom M." <courir26@yahoo.com>
Subject: Re: [R-390] R-725, How To Make Your Own

Ferrite beads, where? I have the R-725 drawings and there are no ferrite beads
to be found. Also the tuned circuit IF decks were specially made for the R-725.
They did not use decks from the R-390 (although I have done that myself and it
works great). Here are the simple steps necessary to roll your own R-725 style IF
deck form a junker R-390. Winter is coming. Everyone needs a good project.
IF deck tips                                     page 214

Date: Sun, 21 Aug 2005 16:14:25 -0700 (PDT)
From: "Tom M." <courir26@yahoo.com>
Subject: Re: [R-390] R-725, How To Make Your Own

>Ferrite beads, where? ......................

The main difference between a R-725 and the R-390A is that the R-725 utilizes a
custom built IF deck that is very similar in construction to the R-390 IF deck. It
has tuned circuit selectivity instead of mechanical filters. The mechanical filters of
the R-390A created distortion when that radio was employed for radio direction
finding use.

Motorola was awarded a contract in 1956 (476-PH-56-91) to prototype the R-
725. I know of a couple of these Motorola sets exisiting today. Packaging of
modified sets for quantity DF use were handled by Arvin Industries and Servo
Corporation of America. Approximately three hundred R-390A's were modified
to the R-725 configuration. New IF decks were manufactured by the
modification companies (actually salvaging some of the components from the
now junker R-390A IF decks) and installed in existing R-390A's. The new IF
decks were named "SERIES 500 IF STRIP ASSY." They looked almost just like R-
390 IF decks except that the IF connectors were relocated to match the cables and
connectors in the R-390A chassis. The circuits were designed to plug and play in
the R-390A instead of the R-390. The R-390 IF decks are not interchangeable in
the R-390A (until now that is, after perfoming the modification described herein).
Notwithstanding DF capabilities, a side benefit of the SERIES 500 deck is that it
provides a smoother sound than does the stock R-390A IF deck. Mechanical
filters are said to "ring" and after a while can be fatiguing to the listener. The
purpose of this procedure is to describe how one may "roll his own" SERIES 500
IF deck from a surplus R-390 IF deck. Please note that I don't advocate trashing
of a good R-390 to do this mod. The IF deck I started with came from a
Motorola junker. I would urge you to likewise find a junker R-390 as a source of
an IF deck for this project. Make sure that the deck is in working condition prior
to beginning the modification.

The R-390 IF deck was designed to operate with one 25V filament supply
(unfortunately the 25V supply available in the R-390A is insufficient to power all
of the filaments in the R-390 IF deck). The R-390A deck was designed to operate
with a combination of 6.3V and 25V filament supplies. The task involved in this
conversion is to rewire the R-390 filaments to comply with the voltages available
in the R-390A and provided at the main IF deck connector, plug and play,
without the addition of any new power transformers. Each of the twelve tubes in
the R-390 IF deck must be addressed for full compliance with the voltages
available from the R-390A. We will also drop the B+ a bit.

Plug P112 of the R-390A shall be plugged-in to the R-390 IF deck at jack J517.
There is much commonality here, except for the connections mentioned herein.
In general, you will be converting 25V series connections into 6.3V (herein
referred to as 6V) parallel connections for most tubes, and moving the
IF deck tips                          page 215

connections of the BFO/PTO/ballast tube series to a different connection point in
jack J517. The 6V filament supply shall be provided to the R-390 deck by
pin 20 of P112 from the R-390A.

General instructions: Refer to the schematic for the original R-390 as the "before"
schematic. Use the best soldering technique you can in this limited access space.
Don't insulate or bind any wires until instructed to do so. You will be utilizing
some of the new 6V supply connections more than once. Make sure you can
recognize your new wires. I used black wire for the 25V supply, red wire for the
6V supplies, and green wire for new grounds. The first task is to install a B+
dropping resistor to better match the 180V B+ that the R-390 IF deck is expecting.
To do this, locate inductor L503 under the IF deck. This will be found snapped
into a holder right above pin 2 of J517. Disconnect one end of the coil, and install
in series with it (the equivalent of) a 470 ohm 2 watt resistor. This will tame the
B+. The first tube circuit we'll work on is the ballast tube circuit.

V508 (5749) and RT512 (3TF7) These must be supplied by the R-390A 25V
filament supply. To do this, sever the connecting wire at pin 8 of jack J517
(underneath the deck) to free this slot up (hint: save access to the connector end
of the wire as you will use it to wire supply to V509). Then, sever the connection
at pin 2 of RT512 and wire this pin to pin 8 of J517 of the R-390
deck with a long piece of new wire. The filament return connection remains
unmodified. This modification will make the BFO/PTO/ballast tube series
connections identical to the R-390A 25V filament supply connections. As
mentioned above, this 25V supply is insufficient to supply the remainder of the
tube filaments, thus the need to employ the 6V supply for this task.

The following 6V tubes shall have filaments wired from the 6V R-390A supply.
The filament pins of these tubes are pins 3 and 4. Don't sever any connections
unless instructed to do so. The modification will use as much existing R-390 IF
deck wiring as possible (and thus may seem a bit screwy to you untilfinished).
V504 (6BJ6) 6V will come from its existing connection at pin 4.

Ground will come in the next step.

V503 (6BJ6) Wire pin 3 of V503 to pin 4 of V504 for 6V supply.
      Ground V503, pin 4.

V502 (6BJ6) 6V supply will come from an existing connection at V503, pin 3.
      Ground V502, pin 3.

V501 (6BJ6) Sever ground connection at V501, pin 3 and
      wire pin 3 to V502, pin 4.

V505 (6AK6) 6V supply will come from existing connection at pin 4.
      Ground will come in the next step.

V506 (6AK6) Ground pin 4 of V506. Wire pin 3 of V506 to pin 4 of V505
      for 6V supply.
IF deck tips                           page 216

V509 (6BJ6) Locate the free wire which was cut from underneath J517,
      pin 8, and connect it to the 6V filament supply at J517, pin 20.

The following tubes are 12AU7's wired in various series schemes in the R-390.
They must be rewired according to their 6V option for use in the R-390A. Note
two of the connections require dropping resistors on the 6V source of V507 and
V510 to obtain the desired 5.3V filament voltage.

V511 Sever ground connection at pin 5.
      Connect pins 4 and 5 together for 6V supply, ground pin 9.

V507 Sever connections at pins 4, 5 and 9, including the two resistors (one
       120 ohm and one 22 ohm). Wire 6V supply from your previous work at
       V505, through the deck opening for variable capacitor C525, to pins 4 and
5 through a 3.9 ohm, 1 watt resistor. Ground pin 9.

V 510 Sever connections at pins 5 and 9.
       Ground will come from existing pin 4 connection.
       Remove 120 ohm resistor between pins 4 and 9.
       Wire pin 5 to pin 4.
       Wire 6V supply from J517, pin 20 to V510 pin 9 through a 3.9 ohm, 1 watt

There are no changes to any of the other connections in the R-390 deck. Prior to
installing the modified R-390 deck in your R-390A, you must check your work.

Perform continuity checks from J517, pin 8, with RT512, pin 2.

Perform filament supply and ground continuity checks as follows. Note: There
will be more than one ground connection at various tube sockets, but the
filaments should have continuity exactly as shown.

Filament supply is checked from J517, pin 20.

V501, filament,   pin 3; ground, pin 4.
V502, filament,   pin 4; ground, pin 3.
V503, filament,   pin 3; ground, pin 4.
V504, filament,   pin 4; ground, pin 3.
V505, filament,   pin 4; ground, pin 3.
V506, filament,   pin 3; ground, pin 4.
V507, filament,   pins 4 and 5; ground, pin 9.
V509, filament,   pin 4; ground, pin 3.
V510, filament,   pin 9; ground, pins 4 and 5.
V511, filament,   pins 4 and 5; ground, pin 9.

Now insulate any bare connections, and use mini-tie wraps to secure the new
wires to sturdy nearby points. To enable final installation of the deck in your R-
390A, you'll need to make two adapter cables. These cables shall consist of
IF deck tips                                     page 217

jumpers (RG-59 is OK, approximately eight inches in length) with BNC's on each
end. You'll also need two adapters of the type found on the back of the frame of
the R-390A at the IF OUT jack (AMPHENOL 47200). This will provide crossover
from MB connection (R-390A standard)to BNC (R-390 standard). Connect P-218
of the R-390A to J-526 of the R-390 IF deck with one of the cables. Connect P-213
of the R-390A to J-525 of the R-390 IF deck with the other cable. It is a good idea
to label these cables.

Install the deck in your R-390A. You will notice that the screw holes are the same
as for the R-390A IF deck, however the screws of the R-390 deck are of larger
diameter. I did not change these screw as they are captive into the deck. The
BFO, BANDWIDTH, and power connector of the deck will hold it in place,
however I would not install it in a Jeep this way. Changing these screws is

When you turn on the power, make sure your dial lamps light up normally. If
they don't, you have a filament supply problem so turn off the set immediately
and troubleshoot. For great sound, instead of using the built in audio deck, I
prefer to tap the audio from the diode load jumper at the back of the set.
Through a 0.1 uF or larger capacitor, feed this signal into your line audio amp of
choice, and enjoy the tuned circuit audio of the new R-725, errrr, R-390A with
tuned circuit IF. You'll get the smooth sound of the R-390 and R-725, but have
the parts availability and support common to the R-390A for the balance of the
set. I've used my modified IF deck in two different R-390A frames, and it
worked equally well in both. In my opinion, it makes the long term listening
experience much more enjoyable. If you have any questions about the mod,
please feel free to write.
Date: Sun, 21 Aug 2005 20:21:13 EDT
From: ToddRoberts2001@aol.com
Subject: Re: [R-390] R-725, How To Make Your Own

Thanks for the great step-by-step directions to convert an existing R-390A into
an R-725 "clone" using an R-390 IF deck. I have a spare R-390 IF deck I have been
saving for just such a project so it will be a breeze using your instructions for the
conversion. This will make a good late-summer project also.
Date: Sun, 21 Aug 2005 20:34:33 EDT
From: Llgpt@aol.com
Subject: Re: [R-390] R-725, How To Make Your Own

I never had any ferrite beads on the R-725/URR I had, it did have the mu metal
shields around the PTO though. Mine was an Arvin Industries version, s/n 95
Les Locklear
IF deck tips                                     page 218

Date: Mon, 22 Aug 2005 08:41:01 -0400
From: SRosenberg@nyiso.com
Subject: [R-390] IF module C553

I have a two R390a's. One is a EAC 67 vintage. I was checking the IF module for
"Black Beauties". The C553 is a silver hermetically sealed cap made by West. Are
these risky to be left in place?? The other R390a is an original Collins single fuse
model. I'm going to install the separate B+ fuses but the question is does this
effect the value of the radio? I was thinking of putting the fuses on a bracket
inside the radio as opposed to drilling holes in the rear panel.
Date: Mon, 22 Aug 2005 10:48:31 -0400
From: "Tim Shoppa" <tshoppa@wmata.com>
Subject: Re: [R-390] IF module C553

I don't think any manufacturer ever put a black beauty in for C553.

Your Westcap is spec-wise just the same as the Sprague hermetic cans that I've
seen in other IF strips, and should be replaced with a new high-quality
conservatively-rated cap. I like the orange drops but physically much smaller
polyester caps ought to be fine too.

> The other R390a is an original Collins single fuse model. ....<snip>

Usability and safety-wise, the fuses are a way good idea. Without it a tube
arc/short can take out some chokes and, worst case, start a fire. But they'll
reduce the rarity of a completely-non-modded radio. It'd be interesting to know
this history of this radio. Most of the ones in military use got modded to three
fuses when they went through the depot many decades ago. But maybe this
was a MARS or non-military (embassy, contractor equipment, ?) unit from the
Date: Mon, 22 Aug 2005 14:31:40 -0700
From: "David Wise" <David_Wise@Phoenix.com>
Subject: RE: [R-390] R-725, How To Make Your Own

I want to apologize in advance if I am bringing up something that was resolved
in the past. If it was, just say so and summarize the result. Tom mentions below
that most of the mod consists of rewiring the '390 deck for 6.3V heaters because
"the '390A can't handle the 25.2V load". Might that not be an issue if you didn't
run the ovens? As we all have sworn :) never to do? I haven't done the math. If
you think this is viable, how about an abridged procedure that leaves the deck
series-wired? It would be a LOT less work.
IF deck tips                                     page 219

Date: Fri, 2 Sep 2005 10:16:08 -0700
From: Dennis Wade <sacramento.cyclist@gmail.com>
Subject: [R-390] AGC Problem Returns

After finding (I thought) the problem with my AGC in the 390A, it seems now to
have returned. To recap the original problem briefly: Observed low no signal
voltage on the line (just about 0, maybe slightly negative) instead of the spec'ed
-0.4. Replaces V509 and no signal condition became as spec'ed. Noticeable
improvement in audio quality. Then I proceed to do a full alignment with very
good results. Radio burns in on the bench. Problem develops.

Now: No-signal AGC is back near 0, at about -0.08 to -0.10. Noticeable
distortion, especially on very strong signals. AGC only develops about -7 volts
on the strongest BCB signal (>80 on the carrier meter). Sounds like something is
loading it again. My question is more how to isolate it to a particular stage. If I
look at the signal grids of all the controlled tubes (IF and RF decks), will the
offending stage be obvious, or will all the grids look the same since they are all
on the controlled line. And, is it correct that if I'm looking at a low resistance on
the AGC line, that I can isolate it to the RF or IF deck by pulling the IF connector
and observing what if any change. Would the components around V509 be likely
suspects? And probably the most elementary of all: I've been assuming that the
resistances given in the voltage/resistance diagrams are with the module in
question fully connected to the rest of the radio...right? Just looking for some
hope..I'm hoping I don't end up digging for capacitors in the IF deck. :(
Date: Sun, 4 Sep 2005 20:43:33 -0700
From: Dennis Wade <sacramento.cyclist@gmail.com>
Subject: [R-390] AGC problems - need help interpreting IF resistance eadings

Spent some time today checking resistance values on the AGC line in the IF deck.
Definite problem on the AGC bus. Where the AGC bus comes into each of the
controlled stages in the IF deck:
       V501 grid Pin 1 110K, should be 500 K
       V502 grid pin 1 70K should be 500K
       V503 grid pin 1 110K should be 500K

Obviously something is leaking badly...I checked C512 (bypassing the AGC line
in the grid circuit of V502) thinking since that's the stage with the lowest
resistance, that would be the problem. But, you guessed it..C512 is fine. I lifted
the ground end and the AGC line resistance to ground didn't change. Just for
kicks, I put the ohmeter across C502 and C519 (AGC line bypasses in V501 and
V503 stages), and didn't see anything but the 110K to ground. Was that a useful
test, or do I need to actually lift one end of those guys and check for sure. What
else should I be looking at in the IF deck that could be loading down the AGC
line?? I running out of ideas..what am I overlooking?
IF deck tips                                     page 220

Date: Sun, 4 Sep 2005 22:35:42 -0700
From: Dennis Wade <sacramento.cyclist@gmail.com>
Subject: Re: [R-390] AGC problems - need help interpreting IF

> Also remember that the mechanical filters are on that line <snip>

I have the IF deck out of the chassis, so I'm pretty confident the leakage is in the
deck. Would a leaky filter otherwise perform normally? In order to isolate a
filter, do I need to disconnect one or both ends? Is it possible to disconnect all of
them at once by lifting the common ground? (if I can find it).
Date: Mon, 5 Sep 2005 14:48:49 -0700
From: Dennis Wade <sacramento.cyclist@gmail.com>
Subject: Re: AGC problems - need help interpreting IF resistance readings

Well, I think I've isolated the problem to the output side of the mechanical filter
group, so its either a filter, a mica cap (unlikely, since the filter would have to be
leaking to ground too), or the switch itself. I want to go over my reasoning
before I start lifting wires off the filters.

I'm still a novice at troubleshooting (won't be able to use that one for much
longer). I lifted the filter end of the 22K, R507 from the rotor of the switch. This
isolates the grid circuit from the AGC line. I still see about 120K from the rotor,
and pin 1 of V502 to ground.

The pin 1's of V501 and V503 now show infinite resistance to ground. There is no
DC path from input to output of a mechanical filter, correct? Does what I see and
conclude pas the laugh test so far?
Date: Mon, 05 Sep 2005 18:03:46 -0700
From: John Kolb <jlkolb@jlkolb.cts.com>
Subject: Re: [R-390] AGC problems - need help interpreting IF

>There is no DC path from input to output of a mechanical filter, correct?.........

Correct, the input coil will measure somewhere around 50-60 ohms, as will the
output coil, but infinite between the pair. Also, should be infinite between either
coil and filter case (out of circuit)
IF deck tips                                     page 221

Date: Mon, 5 Sep 2005 20:21:36 -0700
From: Dennis Wade <sacramento.cyclist@gmail.com>
Subject: Re: AGC problems - need help interpreting IF resistance readings

Thank you everyone for your responses.

The 8 Kc filter had a high resistance (~120K) short to ground.

When I opened up the filter box, I discovered why the 16 kc filter was out of the
circuit..it has about 5K from ground to either terminal. And, one side was still
wired into the common side of the filters! That helped me discover the hard way
that I needed to isolate BOTHterminals (duh) since one side is all wired in
common in order to find the second suspect filter. I also discovered that the tabs
on the trimmers will only flex so many times before breaking. One got flexed
one too many times...luckily it was the one for the 8kc filter. So, I put shrink
tubing on the exposed wires and hooked up the remaining working ones and
fired her up. Sure enough, no more distortion on strong signals, and overall an
improvement in audio quality. Well, if I had to lose 2 filters, I guess those would
be the two to lose (for my listening anyway.) I don't feel a need to replace those
filters right away. I happen to have an 8 and 16 kc Clevite ceramic filters, and a 4
kc as well. I'm also wondering as I type this if there may be other filter options
which would give me more flexibility. (note that this particular '390A has the
"factory" SSB mods done on it). Comments are welcome. Thank you all again for
your help.
Date: Tue, 06 Sep 2005 00:08:08 -0700
From: John Kolb <jlkolb@jlkolb.cts.com>
Subject: Re: AGC problems - need help interpreting IF resistance readings

Well, of course, more flexible filter options would depend on your interests. A
good match for the factory SSB opbion would be to install USB and LSB filters.
For more general SWL listening, a 3 and 6 kHz filters would be nice. For TTY or
CW??? The trick is to either find filters with a 100 kohms in and outZ or match to
the newer filters which are typically 2 kohms.

It appears that all the F455Y-xx filters Y-31, Y-60, Y-120, etc are 100 kohms
centered on 455 kHz. Since the "Y" size case filters are round, but smaller than the
"N" case filters, an adapter can be made to hold them and provide good
shielding. Mounting the rectangular style filters would be more of a problem. "Y"
series filters show up on ebay from time to time. The rectangular style filters
would be harder to mount. The "V" case filters, metal, would provide better
shielding than plastic filters such as the "FA" series, and most of the "V" filters
have extremely good shape factors. One could, of course, buy new filters in an
"N" sized case from Dave Curry, but a couple of those would set me back more
than I paid for my 390 :) There are Motorola mechanical filters for sale on my
site if you decide on something a little closer to original than the Clevite ceramic
IF deck tips                                     page 222

Date: Thu, 29 Sep 2005 10:18:31 -0400
From: Joe Fallon <joe.fallon@philips.com>
Subject: [R-390] Whitewater mechanical filter

Came across a Whitewater electronics 8KHz filter P/N F455 X8 in the same
form factor as the Collins filters in the R390A. Anyone familiar with this part and
how it stacks up against the Collins brand?
Date: Thu, 29 Sep 2005 23:08:26 -0700
From: John Kolb <jlkolb@jlkolb.cts.com>
Subject: Re: [R-390] Whitewater mechanical filter

Don't have any in stock at the moment, but the Whitewaters I've seen look
identical to the Collins. I believe they put their labels on filters manufactured by
Collins. Motorola filters, on the other hand have a different style terminal, clearly
not an exact copy.
Date: Sat, 08 Oct 2005 21:54:05 -0700
From: James Cottle <jim_cott@earthlink.net>
Subject: [R-390] How to free stuck IF slugs?

OK, so I finally got around to doing an IF alignment on my R-390A. On the first
fixed IF transformer, the primary slug (bottom) moves so that I can peak the
diode load at 455Khz. The top slug, however, is stuck to where an unsafe
amount of torque will still not allow me to turn it in the coil form. What does one
do to free these ferrite slugs in the coil form? I know that turning it with force is
definitely NOT the answer, for that has been known to crack the coil form. I am
left with the question: Does anyone have a tip in how to free these slugs? I know
they are normally tight, but should not be immovable. I had the same problem
with the single slug form T208. All I want to do is peak T203 and T208 I think
these are the numbers...not messing with the staggered IF transformers) Any
help would be appreciated.
Date: Sun, 9 Oct 2005 08:27:43 -0700
From: "Craig C. Heaton" <wd8kdg@worldnet.att.net>
Subject: RE: [R-390] How to free stuck IF slugs?

Sounds as if the slug is already cracked. Try using a small pick, etc. and clean the
top of the slug. You might now be able to see or feel crack/cracks in the slug. If
this is the case; time to shop for a new/used IF transformer. Others have been
lucky and used a alignment tool with a dab of super glue and the slug has
moved/peaked after the glue dried and pulled the slug away from the ID of the
coil. I had this same issue on T101, don't have the manual in front of me, could be
another transformer. Anyway, someone on the forum listed a transformer and
some RF slugs for sale a couple months after finding the cracked slug. Just what
dad needed! Another option if a spare transformer is available/found; a root
canal. Use progressively larger drill bits drilling out the stuck slug and replacing
it with a slug from the other transformer. Good luck, it can be fixed.
IF deck tips                                     page 223

Date: Sun, 9 Oct 2005 10:10:52 -0700
From: Dennis Wade <sacramento.cyclist@gmail.com>
Subject: Re: [R-390] How to free stuck IF slugs?

If your slug is actually cracked and not just a binding problem...stop here. This
probably won't help you. I had a similar problem with the AGC transformer that
binded before I could complete the adjustment. I found a tip in the Pearls that
worked quite well. Put a VERY small shot of WD-40 into the top of the
transformer and let sit overnight. Problem solved (for me)
Date: Sun, 9 Oct 2005 13:24:15 EDT
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] How to free stuck IF slugs?

Before you put to much effort into tweaking a core, make sure it needs to be
tweaked. If it ain't broke don't try en fix it. There is a good chance the core is
peaked from a previous alignment.

Put 150 uv at 455 into the IF deck and determine if you can get - 7 volts on the
diode load. With 30% modulation, you should get 1/2 watt out of the local audio
across a 1 watt 600 (580) ohm resistor. Between turning the modulation on and
off you should get 30 DB difference in the signal plus noise to noise. This
procedure is in the TM and the Y2K manual for setting up the IF deck. Changing
tubes will get you more than adjusting the transformers. Back in 68 - 75 doing
two a day we almost never tried to adjust the transformers. I have done the
transformer adjustments and yes it will get you a little or lot more output.

If you do need a transformer or slug, list the one you need here. Fellows have
spare parts decks and may be able to help you. Have no fear. If you break it, it
can be replaced. You can do it your self. Or you can ask here if someone local to
you can do it. Pull the cover off the transformer and do the inspections as Craig
detailed above. If the problem is in a bottom slug, you can run the top slug out
of the coil form and look at the bottom slug. Some times the bottom slug can be
run out of the bottom of the coil form through the chassis to allow you to look at
the bottom end of a top slug.

You can get the hair dryer and warm the coil core up to melt some of the wax.
While it is warm you can run the slug up and down to "recut" the threads
through the wax. As it cools keep the slug moving. If it gets tight again stop. Try
to warm the core up and set the slug while the wax is hot.

Some have tried a small diameter long tip on a low wattage solder iron to warm
a slug.

Some have tried to warm the whole deck in the oven at 200 degrees. This leaves
the whole deck looking real shiney. Some like to put the deck in the dish washer
before it goes in the oven. You see folks paying big bucks on E-pay for these
cosmetic operations. Along the way, the heat will let some stuck parts come free.
IF deck tips                                     page 224

The process is mostly non invasive, below the melting point of solder.
Considering what the Julian Creek Receivers were exposed to, a trip in the
dish washer and oven is gentle cleaning.

Thinking of the number of decks I dunked into the teletype and typewriter (mill)
cleaning tank, running a deck in the dish washer is fairly benign.

Do not try a bunch of solvents. The boat anchor folks have threads about all
kinds of things and ways to dissolve coil forms.

If you have to drill your slug out and the replacement slug does not hang in for
adjustment you have two options. One is some bees wax melted into the coil
form. Second is a small chunk of rubber band. The band from an old golf ball
works. A rubber band can be sliced down for a small square strand that will also

Someone talked about having a nice white power used by magicians to dust card
decks and make them very slippery. Motorola used to provide the stuff to their
technicians for use on slugs and in coil forms. The stuff is finer than talc and stays
slippery when moist. The stuff a magicians power was cited as you are likely to
find it in a magic shop. Magic shops being more prevalent than electronic parts
shops these days.                            Roger KC6TRU
Date: Mon, 10 Oct 2005 12:20:56 EDT
From: N4TUA@aol.com
Subject: [R-390] More stuck slugs

I finally have reached the point of doing the fixed IF alignment and guess what.
You got it. Stuck IF transformer slugs. I have inspected them closely and do not
look to be cracked or broken. Are there any ideas from the group on how to get
the slugs turning again? How about the WD-40 idea? I have two that will not
turn T501 and T502. Any and all help would be greatly appreciated.
Date: Mon, 10 Oct 2005 11:29:54 -0500
From: "Barry" <n4buq@aol.com>
Subject: Re: [R-390] More stuck slugs

I haven't tried it, but I have heard that *gentle* heating of the slug by heating the
tool used to adjust it and inserting that into the slug sometimes works. I would
think you could also *gently* heat the entire xfmr with a hair dryer and that
might help too. Good luck with it.
Date: Mon, 10 Oct 2005 10:02:27 -0700
From: Dennis Wade <sacramento.cyclist@gmail.com>
Subject: Re: [R-390] More stuck slugs

Although I had good results with the *very* small shot of WD-40, I would
exhaust other mechanical/thermal means before I tried that.
IF deck tips                                     page 225

Date: Mon, 10 Oct 2005 13:22:27 -0400
From: "Patrick" <brookbank@triad.rr.com>
Subject: Re: [R-390] More stuck slugs

If the slug is stuck, it must not have been moved for a long long time, that means
to me that it is in alignment, leave it alone.
Date: Mon, 10 Oct 2005 13:29:51 -0400 (EDT)
From: John Lawson <jpl15@panix.com>
Subject: [R-390] Re: More stuck slugs

Am I mistaken in my dim remembrance that some ferrite slugs were
impregnated with a paraffin compound to aleviate just this problem? And, if I
am correct, is it possible that high-end radios of this era used them? Just
something I recall from over 4 decades of Junque Collecting...
Date: Mon, 10 Oct 2005 13:31:22 -0400 (EDT)
From: John Lawson <jpl15@panix.com>
Subject: Re: [R-390] More stuck slugs

>.......it is in alignement, leave it alone.<snip>

Unless (as is the case here) you've changed tubes, or otherwise disturbed the
Date: Mon, 10 Oct 2005 13:39:49 -0400
From: "Patrick" <brookbank@triad.rr.com>
Subject: Re: [R-390] More stuck slugs

Then check the tubes and/or return the disturbed circuits back to what they
were, the problem, if any, should be there and not with the slug..
Date: Mon, 10 Oct 2005 13:51:09 EDT
From: N4TUA@aol.com
Subject: [R-390] IF slugs

I am getting some good input on the stuck slugs and I am tending to just leave
them alone. I would wonder though if one was going to do the fixed IF
alignment. How do you get to those bottom slugs? What type of tool do they
take? I would think the tool would be smaller than the hole in the top slug and
would go down through to adjust the bottom slug. What type of tool does it
take? None like I have that is for sure. Thanks for the help, Collin
IF deck tips                                     page 226

Date: Mon, 10 Oct 2005 13:25:40 -0500
From: "Barry" <n4buq@aol.com>
Subject: Re: [R-390] IF slugs

The typical adjustment tool has a short tip that has the hex shaped business end.
Further down the shaft, the tool relieved to a sufficiently small enough diameter
to clear the hex shape from the "upper" slug. I hope that makes sense...
Date: Mon, 10 Oct 2005 15:01:09 -0400
From: "Patrick" <brookbank@triad.rr.com>
Subject: Re: [R-390] IF slugs

The IF transformers normally require no adjustements, however, if you are set
in adjusting them, follow the procedures outlined in "The 21st Century R-
390A/URR technical reference" a collection of wisdom for enthusiasts, paragraph As far as an adjustement tool, with a little patience, you can fashion a
good one out of a bamboo skewer. If you narrow the shaft so that it can go thru
the first slug, then the second slug can also be adjusted. Be aware that the
instructions for this adjustement requires that resistor R504 should be 560
ohms.Again I stress that unless one of the transformers have been replaced, I
would not adjust any of them, contrary, if any transformer has been replaced I
would adjust all 3 of them. Back to the old proverb "if it is not broken, do not
mess with it"
Date: Mon, 10 Oct 2005 17:37:18 -0400
From: "Drew Papanek" <drewmaster813@hotmail.com>
Subject: [R-390] Re: More Stuck Slugs

It may or may not be in alignment depending on motion, drifting capacitors, and
aging characteristics of the core material. Core permeability tends to decrease
with aging and hence inductance drops. But this is an R-390A we are talking
about. The bandwidth is determined by the mechanical filters and the IF is
otherwise broadly tuned; exact adjustment is not critical. Yes, if maladjustment
were to cause the IF to become broader then the IF's noise contribution would
increase, but by how much. The R-390A 's IF has far more gain than necessary
and so we reduce it by use of the IF gain control. There is sufficient reserve gain
to compensate for a little IF misalignment.
Date: Mon, 10 Oct 2005 19:44:54 EDT
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] Re: More stuck slugs

As a radio repairman from 68-75 I did some things to R390/URRs R390A/URRs
that I will not even repeat. From these "experiments" I can assure you there is no
paraffin compound that will soften or dissolve in a petroleum base solvent, in the
R390 slugs. I cannot say about other items as I was not subjecting them to
"experiments" in removing living growths from the interior.
IF deck tips                                     page 227

Date: Mon, 10 Oct 2005 20:27:07 -0400 (EDT)
From: John Lawson <jpl15@panix.com>
Subject: Re: [R-390] Re: More stuck slugs

I have miscommunicated. What I was referring to is that, over the years, I have
encountered IF slugs that appeared to be imbued with some form of waxy
lubricant - and since these were generally very old devices, I assumed (and y'all
*know* what you get when you assume) that the substance exuding from the
ferrite core was wax, paraffin, whatever. Haven't seen that many - I do have a
few hundred IF and other 'cans' around here - I'll paw thru some and see if I'm
remembering correctly, or if it's just another one of them damn Hippy-Era
Flashbacks... ;}
Date: Mon, 10 Oct 2005 21:41:32 -0400
From: "Dave Maples" <dsmaples@comcast.net>
Subject: RE: [R-390] Re: More stuck slugs

All: If the R-390A hits the target for sensitivity, I'd leave it alone. The urge to
tweak is strong, but if it's hitting the spec target, and there's a chance to tear the
thing up by tweaking, the logical (but not emotionally satisfying!) thing to do is
leave it alone... Just my own opinion, of course.
Date: Tue, 11 Oct 2005 21:22:24 EDT
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] Re: More stuck slugs

Not all slugs are R390 slugs. I'll bet you have encountered some that were wax
impregnated or not exactly as robust as R390 slugs. Other slug from other radios
are likely to be compsed of almost anything. I just wanted to point out that I had
never encountered a R390 or R390A slug that would dissolve.
Date: Mon, 17 Oct 2005 02:54:08 -0400
From: n4tua@aol.com
Subject: [R-390] Fixed IF stuck slugs

I have received many helpful ideas on this subject and would like to thank
everyone who added to my question. I have decided to leave the stuck slugs
alone for now anyway. I will continue to look elsewhere for the cause of the low
sensitivity. Any ideas on this? I do receive signals that are low in volume with
the rf gain turned to 100%. Also seems to be a loud noise floor. Almost like the
noise is as loud or louder than the signal. Any help would be appreciated. Sure
don't want to have to change those fixed IF cans.... :'- (
IF deck tips                                     page 228

Date: Sun, 27 Nov 2005 13:22:02 -0500
From: Glenn Little WB4UIV <glennmaillist@bellsouth.net>
Subject: [R-390] Incomplete IF module

Some years ago I bought an incomplete IF module from a surplus house. In
cleaning this weekend, I uncovered it.

The module is marked: SM-C-343621
I.F. FINAL ASS'Y FR-11-C22-C-4-26418(E)                        SER. NO. 0294

The module has the tube sockets, RF connectors, T5-1-T503, Z501, C506, TB501
and some small parts mounted. Very little has solder on it. Is this a rare find?
Why would it have the serial number assigned before completion?
Date: Sun, 27 Nov 2005 13:55:53 -0500
From: shoppa_r390a@trailing-edge.com (Tim Shoppa)
Subject: Re: [R-390] Incomplete IF module

Is it possible this was not a "half-built" module but a "built, torn down for spare
parts, and the begun to be rebuilt" module? For reasons that I do not fully
comprehend I've seen lots of stripped-down IF modules over the years, almost
always missing the BFO and often missing some other parts.
 Date: Sun, 27 Nov 2005 16:26:34 -0500
From: Glenn Little WB4UIV <glennmaillist@bellsouth.net>
Subject: Re: [R-390] Incomplete IF module

 From what I can see, this is a module that was never completed. The filters
appear to have been installed and removed. T503 was never installed ( I
mentioned T503 as installed earlier, this is Z503). J512, R519 and R523 were never
installed. The standoff insulators are installed, but have never had components
soldered to them. There are no marks on the chassis to indicate that the missing
parts were ever installed.
Date: Sun, 27 Nov 2005 15:47:28 -0700
From: Les Locklear <leslocklear@cableone.net>
Subject: Re: [R-390] Incomplete IF module

Lots of those surfaced in the late 80's. In fact, many were marked with an EAC
spare parts contract number. Clavier (who was originally Capehart then finally
Fowler) made some of them also. Tom Marcotte has the list. I'm at work and
don't have that list available.
IF deck tips                                     page 229

Date: Sun, 27 Nov 2005 15:45:55 -0800 (PST)
From: "Tom M." <courir26@yahoo.com>
Subject: [R-390] Comm Systems Corp, was Incomplete IF module

Your incomplete IF module is from Comm Systems Corp of Morton Grove, IL,
run by a fellow name HM Harper. They "attempted" to make R-390A's from
tooling bought from Stewart Warner, but the tools were in poor condition and
the company never was able to produce full sets that met satisfaction of the
inspectors. The company eventually argued that R-390A's could not be made to
specification (huh?) and that the contract be terminated. The govt took all the
stuff and Comm Systems quit the R-390A business.
Date: Mon, 28 Nov 2005 19:01:17 EST
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] Incomplete IF module

The question was why do we find serial numbers affixed to modules before the
guts get soldered into the subassembly?

We need to go back to the manufacturing process. As one is building items
during the day, something must be done to track productivity to keep modules
from getting shuffled and counted as production. The sheet metal was often
stenciled and varnished before assembly stated. That way new people had some
clues by looking at the chassis silk screen where they were supposed to install
their quota of parts. As long as you have the critter getting silk screened and
drying, adding a serial number was just part of the same process. This also let
management track production. In the days before copy machines and office
printers, paper work was much different. You got a sheet of paper numbered
from 000 to 999. You put your name and date on the paper. You put a job code
number on the paper. As you built items you filled in the digits for the serial
number in front of the 000 to 999 that went with the item you completed. You
were expected to complete so many assemblies per day for the job code. At the
end of the day you counted how many serial numbers you completed on the
page. Management had a page with numbers and job codes. They placed a date
after the serial number to track production. If a serial number come up on the
same job code from two different days, Management would first track back
through the paper and then through the employees and find out who was
padding their production count. Amazing what one learns in college classes.
Roger KC6TRU
IF deck tips                                     page 230

Date: Thu, 29 Dec 2005 14:22:48 -0700
From: DW Holtman <future212@comcast.net>
Subject: [R-390] Chassis finish

<snip> Another question. Was the modification that installed variable caps (C-
569 through C-571) in the input and output of the mechanical filters in the IF
module applied at Depot during rebuilds, or just put on newly manufactured
modules? The reason I'm asking, there is an IF amp for sale on Ebay without the
variable caps on the IF Module. It went through depot 1982, and does not have
the variable caps. This particular module looks like it has yellow plastic caps?
Ebay item number is 5847326968. I'm just courious about this mod, because I
have two IF modules, one with and one without the mods. Thank you in
advance for any help.
Date: Tue, 10 Jan 2006 08:38:47 -0500
From: Gord Hayward <ghayward@uoguelph.ca>
Subject: Re: [R-390] Open Z-503 AGC IF Transformer

When I got mine, Z503 was open too. I tried to steam (hot air really) the ferrite
off but the whole thing came undone. Not finding a replacement, I took a big
coil out of my junque box, cut the form to fit, added a resonating cap at 455 kHz
and rebuilt the guts of the can. Now it's dead on spec. The trick is to use a small
cap, 20 to 40 pf or so to get the Q as high as possible. That circuit needs the high
Q to get the AGC voltage high enough. Do the resonance check before the
cutting and installation steps.
Date: Tue, 10 Jan 2006 08:52:26 -0500
From: JMILLER1706@cfl.rr.com
Subject: Re: [R-390] Open Z-503 AGC IF Transformer

Believe it or not I have rewound RF/IF transformers like this that have been
fried. If you can unravel the turns, just measure the total length after getting the
wire off, go buy some small diameter magnet wire of the same gauge and
length, or close, and wind it back on. It won't look pretty but it will probably
work. Glue or wax to hold it in place. I did that with an RF coil in a 51S1 once.
Worked great. Alternately, it is possible that a coil from generic 455 khz IF can
would work. JM
Date: Tue, 10 Jan 2006 22:09:41 EST
From: ToddRoberts2001@aol.com
Subject: Re: [R-390] Open Z-503 AGC IF Transformer

An open winding in coil L514 in the Tuned Circuit can Z503 seems to be a
common failure mode in the R-390A IF deck. I have run across several open-
circuited ones over the years. It may be corrosion eventually breaks the tiny
wire leads from the coil or it may be something to do with the insulation
breaking down as this coil has about 180VDC running through it and some
current. If anyone is interested I measured the inductance of L514 in Z503 as
IF deck tips                                     page 231

1.385 mH. This would require a capacitance of 88pF to resonate at 455KHz. I see
that Mouser has some Hi-Q miniature radial inductors with a Q of 100 in a 1.2mH
and 1.5mH size. These would easily fit inside the Z503 can. The 1.2mH inductor
would require 102pF to resonate at 455KHz and the 1.5mH inductor would
require 82pF. The peak may be broad enough that you could get by with a fixed
cap across the coil but one could also mount a miniature trimmer cap and a
slightly smaller fixed cap inside the can to get the best peaking on the coil. I
haven't measured the Q of the original coil yet but I do have a Heathkit Q-meter
and I will check it out. I would think a coil with a Q of 100 would be suitable here.
In the future the Z-503's are going to be hard to find. It would be nice if an 80
cent inductor from Mouser and a small mica cap would get it working again.
Date: Fri, 13 Jan 2006 14:43:01 EST
From: ToddRoberts2001@aol.com
Subject: Re: [R-390] Open Z-503 AGC IF Transformer

If anyone is interested here is a recap of the measurements I took of the tuned
circuit Z-503 inductor coil L514. I measured the inductance of the coil as 1.385mH.
I also had a chance to measure the Q of the Z-503 coil L514 and I was surprised to
find it measured a very low Q of only about 30-40 Q at 455KHz on the Heathkit
Q-meter. I have a bag of small 1.2mH molded inductors I picked up a while ago
from Hosfelt Electronics and measured one and its Q was about 60 at 455KHz so
it looks like just about any small commercial inductor would work fine to get Z-
503 working again. I think those inductors only cost me about 20 cents each. I
found it took about 85pF to resonate the 1.2mH inductor at 455KHz, so a typical
small Mica cap would work well across the inductor to get Z-503 working again.
Best to use something like a Heathkit Q-meter to determine how much capacity
is needed to resonate the new coil at 455KHz due to the unknown distributed
capacity of different inductors. If someone ever needed help with a burned out
Z-503 I can mix and match small inductors with a small cap to resonate at
Date: Sun, 15 Jan 2006 10:27:41 -0500
From: shoppa_r390a@trailing-edge.com (Tim Shoppa)
Subject: [R-390] Strange BFO backlash explained!

You guys may remember me asking about a strange BFO backlash that I had
with my yellow striper's IF deck last summer. It manifested itself sometimes, and
not others, and while I had dinked around with it I never thoroughly understood
the cause. Now that I'm putting that deck back together (I had to pull the BFO
reactor to get at and replace the V505 socket, which had crumbled into dust over
the years) I can understand the cause: the shaft of the BFO reactor shifts in and
out a little bit. I don't know if this is "typical" or not, but seeing as how the
internals work it makes perfect sense that this causes backlash. The springy-thing
shaft coupler can be adjusted to provide enough tension over the working range
that this problem is at least minimized. Is the BFO reactor shaft really supposed
to have this much (I'd guess 1/32") wiggle in and out? I'd be very surprised if
IF deck tips                                     page 232

Date: Sun, 15 Jan 2006 15:54:54 EST
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] Strange BFO backlash explained!

We do expect the BFO shaft screw in and out as you tune it. We do not expect the
shaft to have any slop moving in and out so there should be no backlash as you
adjust the BFO. I can believe the BFO bushing is worn to the point where you
have the 1/32 free play in your BFO reactor shaft. Like you said the bellows
coupler can be adjusted to place minimum force on the reactor shaft and the IF
deck BFO shaft bushing. I believe you BFO suffered from years of mis-adjusted
bellows coupler and that has caused a lot of wear on the reactor can bushing and
thus giving you a lot of slop. If you can live with it OK. If not, it is not real hard
to do a reactor can replacement. The reactor cans did die and were replaced.
Date: Tue, 31 Jan 2006 17:45:44 -0600
From: "Cecil Acuff" <chacuff@cableone.net>
Subject: [R-390] IF Trimmer notes

 Discovered something in the last few days that might be of interest. I've not
seen it talked about here in the past. While doing the alignment on my R-390A
project (mostly done R-390's) I have gone through the adjustment of the
trimmers across the mechanical filters. The gain seemed a bit low on the 4 kc
position so I figured it was the dreaded worn out filter scenario. While adjusting
the trimmers for max gain I noticed a couple only had one peak. I would expect
on the trimmers that will rotate 360 degrees to have two peaks. Some had two
peaks and that was on the more sensitive positions.

The ones with only one peak would lead one to believe he had found the correct
position for the trimmer which isn't so. What is in fact the case...the fixed cap is
not the correct value to properly resonate that end of the filter. I substituted
various values in place of the factory cap and found one that would allow
adjustment through two peaks and the gain came way up. After getting all the
top end tuned I pulled the deck loose and stood it up in the radio to adjust the
lower trimmers as my side panel does not have the holes to allow adjustment
while the IF deck is in place. I found three of the four bottom trimmers to have
only one peak. I will have to pick up some more caps to continue the tuning of
the lower end of the mechanical filters but I expect the final outcome to be a
much better performing radio. It should allow me to reduce the overall IF gain
and improve overall sensitivity beyond what I already had achieved by
improving the efficiency of the coupling of the signal through the mechanical

Bottom line is if you only get one peak on the trimmers, improvements in
performance can be achieved by getting the correct value cap in the circuit to
allow proper resonance setting. Can't go by the values in the book as each filter
will probably be different. Two of mine had been changed from the Collins to
the later Whitewater filters....that probably accounts for two positions being out
of resonance. The caps I pulled were 82 pf and tested OK. I also had an
IF deck tips                                    page 233

intermittent gain problem in the 4 Kc position which turned out to be the lead on
the original fixed cap had rotated in the body of the cap causing a change in
capacitance anytime the cap was pushed on....or when the temp. in the radio

This radio is getting close to .1uv a little at a time with most bands running .13 to
.15 @ 8Kc. Not bad for one that came out of the SJC pile!
Date: Tue, 31 Jan 2006 20:10:58 -0600
From: "Barry" <N4BUQ@aol.com>
Subject: Re: [R-390] IF Trimmer notes

Good analysis. I'd assume that with any of the ceramic trimmer types, if you
don't get two peaks (or nulls as the case may be), the cap isn't of sufficient value
due to whatever due to the mechanical nature of their construction.
Date: Wed, 1 Feb 2006 09:25:20 -0600
From: "Barry" <n4buq@aol.com>
Subject: Re: [R-390] IF Trimmer notes

Well, with *some* air variables. The type that have a mechanical stop at
maximum capacitance will only have one "true" peak or null (depending on the
Date: Sat, 11 Feb 2006 19:05:13 -0600
From: "Chuck Curran" <ccurran@wi.rr.com>
Subject: [R-390] BFO Problem/Question for a newly restored R-390A

In April of 2005 I received a R-390A from an Uncle who had decided to hang up
his radio activities at the age of 85. I had given him a 75A-3 about 18 years ago,
which he traded for this particular R-390A. Upon deciding to clean out his
basement, I became first on the list to get the Capehart 1961 vintage R-390A. My
lucky day! This particular radio came complete , all covers present and in very,
very good physical condition. I started by gathering all information, printing out
full sized schematics and then diving in. It had never been touched since it's
departure from the military, as near as I could tell. Seven tubes were so bad, my
Hickok almost threw them back at me. I re-capped the unit, carefully cleaned all
gears with a 100% disassembly. Yea, I messed up, even pulled out the Geneva,
and that took a bit to get re-synced. After picking up a HP606A signal generator,
I was able to properly re-align the electrical end of the radio, and all seemed
pretty good, except that darn BFO! That Heath IG-102 just couldn't handle the

The main problem now is that the BFO would kick in, and then weaken and drop
out within 10-20 seconds. Sometimes it did not work at all, and I had to flip the
switch repeatedly to get it to kick in. O.K., today I decided to determine what
had happened with the BFO circuit. I first checked the resistances on V505
comparing all to the manual values, most were "close" to nominal values, but off
enough to cause a strong interest, especially on pin 5. I then removed the IF
IF deck tips                                     page 234

deck and started to dig in a bit deeper. Upon checking individual resistances I
quickly found that R530, the 22K plate resistor for this Hartley oscillator, had
changed from a correct value of 22K to 33K. That did not seem to be good, so I
installed a new 22K resistor. OK, many of you know how crowded things are
in that part of the 390A. I needed to remove the flexible shaft coupling to access
this area around the V505 tube socket. I successfully replaced this
resistor, using many chunks of solder wick, and then re-installed the IF deck for
a test.

I fired up the receiver, and then tried to zero out the calibration signal at 3.000
MHz- no audio tone at all was heard, but a strong Calibration signal was still
present, at least displayed on the meter. I putzed around, a bit puzzled, since I
had not even heard the normal 10 second long "weak" BFO signal. Where was
it? I spun the dial with the BFO still on and got hammered at 2.987 MHz with a
very strong signal. I turned off the BFO and it disappeared. Tried the Off/On
routine and was able to convince myself I was actually controlling an off
frequency BFO signal. Prior to removing the flexible coupling, I had marked the
BFO sealed unit shaft with a black magic marker dot. I "assumed" I could run
that puppy back to the same spot and all would be well. Wrong, I believe now
that I failed.. During the flexible coupler removal, I realized there were actually
four Bristol set screws, two on either end spaced about 110 degrees apart - gee,
why not 90, was this a manufacturing error for this coupling? Ah, minor detail. I
ended up twisting and cussing, and removed the coupler, without being sure
how much the shaft had rotated. I cleverly told myself that it was surely like a
variable cap, with a 360 degree rotation pattern that would just repeat itself.
Maybe not?

 Here is my question, sorry for the long diatribe. Should I start turning the BFO
shaft until I achieve a tone at the expected points? Is this shaft on a threaded
adjustment, with 3, 4, or 5 turns possible so I can achieve this? As an alternative, I
thought I could try to sample this BFO oscillator output with my frequency
counter, and see where it is. I think I can do this using a tube test socket and just
sample the signal off the available exposed V505 plate contact point. If I am
actually off by 13 KHz, I would want to "try" to turn the shaft to come back to
the correct 455 KHz frequency for the center point of the BFO oscillator. If this
shaft just has a 360 degree adjustment, then I guess I might have a problem,
possibly with the inductor and three caps controlling the oscillator base
frequency. Not likely, since it was on frequency prior to my messing with it.
Being totally and 100% ignorant of the internals of that sealed BFO can, I
hope someone may have learned the construction features and can offer some
advice. Is it a multi-turn adjustment, or just a 360 degree affair?

 In advance, thanks for any comments on this situation, Chuck WA9POU
IF deck tips                                     page 235

Date: Sat, 11 Feb 2006 20:12:03 -0600
From: "Barry" <n4buq@knology.net>
Subject: Re: [R-390] BFO Problem/Question for a newly restored R-390A

I think there are ways to do this without a counter, but I've used a counter for
mine. You can pick up a signal with a loop around the oscillator tube or tie to the
plate circuit through a cap. If you think you might be off by as much as 13kc,
this would get you a *lot* nearer to where you should be with it. I think Roger
has a "radio-only" procedure to set this, but I don't know it offhand.
Date: Sat, 11 Feb 2006 20:46:54 -0800
From: "Craig C. Heaton" <wd8kdg@worldnet.att.net>
Subject: RE: [R-390] BFO Problem/Question for a newly restored R-390A

I think the BFO is a multi-turn device. Hope you have a sig-gen or access to one,
it will be needed, check out Chuck Rippel's web site, link is provided to his IF
Deck Alignment page. At the bottom of the page is the correct way to set the
BFO. His method works, I've used it.
Date: Sun, 12 Feb 2006 01:46:59 EST
From: ToddRoberts2001@aol.com
Subject: Re: [R-390] BFO Problem/Question for a newly restored R-390A

The BFO is a multiturn device good for about 2 1/2 - 3 full turns from end-to-end
of its tuning range, but do not try to force it past its stops, be very gentle with it
as soon as you meet any resistance trying to turn the shaft. I get plenty of signal
pickup for a frequency counter by wrapping 5-10 turns of wire around V504 and
connecting one end of the pickup coil to the freq counter probe tip. Be sure to
turn down the RF gain if using this method or else other IF signals across V504
can give false readings instead of the BFO frequency. Some freq counters may
not have enough sensitivity when using the pickup coil method around V504 so
try whatever works best for you.
Date: Sun, 12 Feb 2006 12:42:43 -0500
From: shoppa_r390a@trailing-edge.com (Tim Shoppa)
Subject: Re: [R-390] BFO Problem/Question for a newly restored R-390A

>... Sometimes it did not work at all, and I had to flip the switch repeatedly....

My guess would be a leaky capacitor that gets worse when voltage is applied (of
course you wouldn't notice it until you turned on the BFO!). IIRC there are at
least a couple of black beauties in that area. One is "just" some sort of bypass on
the current-regulated filament string through the BFO and PTO and is hardly

> that R530, the 22K plate resistor for this Hartley oscillator, had changed
> from a correct value of 22K to 33K.
IF deck tips                                   page 236

Pretty common occurence! Almost all 2.2K plate resistors in my 390A's were up
by several hundred percent. Well, in my yellow striper the BFO oscillator tube
socket was crumbling into tiny pieces of dust. I managed to replace that,
although it was an extended project.

>........with a 360 degree rotation pattern............................

Not. In fact you will notice that the shaft is left-hand threaded, such that when
you turn it clockwise it backs out of the BFO. This moves a slug in and out of an
inductor core. It's also the reason that the flexible coupling is also compressible.

>....Should I start turning the BFO shaft until I achieve a tone .................

Yes. Just don't turn it past its limits, if you're doing all this with a counter then
you will know when you're turning in the wrong direction and not go very far
that way. When you're done, you might want to check the flexible/compressible
coupling to make sure that it's not stretched to its limit either.

>......I thought I could try to sample this BFO oscillator output with my frequency

I do fine with just sticking a scope probe near the tube (may want to remove the
tube shield first). That's enough of a signal to register on my frequency counter
or my scope. Also works great for the crystal oscillators (the bandswitched one,
the 200kHz one, and the 17MHz one.) You can also see the spiky divided-down
100kHz calibrator at the next dual triode in the calibrator too. I know the "classic"
R-390A tuneup procedure only needs signal generators and voltmeters, but if
you've got a scope or a counter then a lot of this stuff becomes trivially simple.
Date: Sun, 12 Feb 2006 19:11:40 -0600
From: "Chuck Curran" <ccurran@wi.rr.com>
Subject: RE: [R-390] BFO Problem/Question for a newly restored R-390A

I just wanted to let you know that the BFO is now running at 100%. Thanks to all
who provided suggestions and comments. I received quite a number of direct e-
mails. Lots of good discussion and some interesting stories about similar
problems too. The first item I had was about the number of available turns, I did
find out that the BFO shaft does have about 3 turns. I needed about 1 1⁄2 to
bring it right back on the money. I used the second method of BFO calibration
to get it right on the money, as shown on page 159 of the TM-11-856A manual. I
am not knowledgeable enough to appreciate why the plate resistor R530 going
from 22K to 33K also changed the resonant frequency, causing the last 45 years
worth of service people to keep twisting it further and further to get a zero beat.
The inductance and 3 mica caps in the can really establish the point for resonance,
I would have expected that a lowering of the plate voltage would have decreased
the output signal amplitude, but left the ,frequency alone. What am I missing in
this Hartley oscillator operational theory?
IF deck tips                                     page 237

It’s nice to now have the calibrator functional for more than 8-10 seconds and a
decent BFO for the rest of the time. I am running out of problems – time to get
a different radio?
Date: Fri, 3 Mar 2006 22:51:29 -0800 (PST)
From: Perry Sandeen <sandeenpa@yahoo.com>
Subject: [R-390] Precision AM Detector Circuit

 I buy an English magazine called Electronics World. It always has a feature of
reader circuits, which usually aren’t applicable to anything I need. However, in
the Jan ’03 issue they had a circuit called "Precision full wave rectifier". This didn’t
peak my interest until I read the last part the said it "will rectify up to about
2Mhz,with input signals as low as 10 micro-volts. I originally used it for full
envelope detection in a 455Khz IF chain."

It uses 7 GASP, WAIL, KNASHING OF TEETH, very cheap transistors, and can
be built on Rat Shack perf board with no sweat. In the same magazine in May ’04
an revamped circuit was done with spice simulation. While it may be tough to
put into a R390, There is plenty of space in a SP600. The first article is a one page
file that is 2.4 Mbyte TIFF image or a 4.8Mbyte RTF doc. The second article is 6
pages long. Each file is about 3.5 Mbytes as a TIFF file. I will be glad to email one
or both to any (PMS Martyrn excepted) who reply off list.
Date: Mon, 6 Mar 2006 22:43:40 -0600
From: "Barry" <n4buq@knology.net>
Subject: [R-390] A bit more on my IF deck

I got the resistors replaced and all seems fine. I need to do a full IF alignment,
but it seems to be behaving just a slight bit better. I'm not sure, but I think it
doesn't take quite as long for the system to dump the charge from SLOW AGC
as it did. Is that perhaps a function of that 2.7M resistor?

I wanted to check the resistances and voltages around where I had worked.
Everything looks pretty good except for pin 2 of V506. According to the manual,
I should have about -0.4V, but I'm getting nothing (HP410B used here).
Checking the resistance, the manual states I should be seeing 500K in AGC mode
and I'm only seeing 400K here. There are three resistors to GND from V506, pin
2 and they add up to 500K. Apparently I have something else parallel to this
that's pulling the resistance down a bit. It's always something.

Any guesses why I don't see -0.4V here?
IF deck tips                                     page 238

Date: 7 Mar 2006 14:12:22 -0000
From: "n4buq@knology.net" <n4buq@knology.net>
Subject: Re: [R-390] A bit more on my IF deck

Okay, I think I'm carrying on a conversation with myself here, but I'll continue...
When I pull the main connector from the IF deck, the resistance at Pin 6 of V506
goes very close to 500K (what the book says it should be). If I reconnect the IF
connector and unplug the RF deck connector, the same thing: 500K.

So, I checked the resistance at pin "E" of the RF deck (the point where Pin 6 of
V506 connects to the RF deck). I get about 1.8M here. Those two resistances in
parallel yeild what I'm seeing at Pin 6 of V506 when everything is connected. I
haven't traced it out, but I assume if I'm supposed to be seeing 500K at Pin 6 of
V506, then the resistance at Pin "E" on the RF deck should be nearly infinite. Any
comments on this?
From: "n4buq@knology.net" <n4buq@knology.net>
Subject: Re: [R-390] A bit more on my IF deck

Okay, more ramblings. Tracing Pin "E" on the RF deck, I see a path through L208,
R232 (22K), R231 (1M), through S207 and then through the selected L22*-2
winding to GND. Therefore, this places a theoretical 1.022M (not includine the
negligible coil DC resistances) across the 500K in the IF deck at Pin 2 of V506. If
this is true, then doing the math, the reading at Pin 2 of V506 should be
approximately 335K. Am I missing something here??
Date: Tue, 07 Mar 2006 11:10:52 -0500
From: JMILLER1706@cfl.rr.com
Subject: Re: [R-390] A bit more on my IF deck

Isn't V-506B the AM detector? If I am reading the schematic right, V-506B
doesn't connect to the RF deck,... I htink it connects to the AF deck (it provides
audio to the AF deck).
Date: 7 Mar 2006 16:44:22 -0000
From: "n4buq@knology.net" <n4buq@knology.net>
Subject: Re: [R-390] A bit more on my IF deck

Oops!!! In my post below, I wrote Pin 6 of V506. I meant Pin 2 of V506A (the
grid of the AGC Time Constant Tube). Sorry.
Date: Tue, 07 Mar 2006 12:43:42 -0500
From: JMILLER1706@cfl.rr.com
Subject: Re: [R-390] A bit more on my IF deck

Let's see.... from pin 2 of V-506 it looks like paths to ground are: R547 (220K) +
R544 (2.7M) to ground thru whatever resistance to ground is in the B+ line in the
power supply. In parallel with: R234 1.5M which is on the AGC line in the RF
IF deck tips                                     page 239

chassis. What's the math for those parallel resistors? I get about 1M, which
doesn't agree with the 500K you're reading...is there another resistance to
ground I am missing? Look all along the AGC line to see if there are others in
the RF deck...I can't find any others. Or am I reading this all wrong ?
Date: 7 Mar 2006 17:59:50 -0000
From: "n4buq@knology.net" <n4buq@knology.net>
Subject: Re: [R-390] A bit more on my IF deck

Pin 2 has a path to ground through R545, R546, and R547 which add up to 500K.
The path through R544 meanders through the system and there are a few paths
to ground I see; however at 2.7M, it is a bit negligible on the overall resistance.
I'm thinking the 500K listed in the manual is theoretically incorrect, but I'm
wondering how close that needs to be. Since I'm not getting the -0.4V on that
pin, I'm trying to figure out why. It may just be a weak tube. I need to try some
subs and also check that pin on my other R390A just to see if I see any
Date: Tue, 07 Mar 2006 13:40:22 -0500
From: JMILLER1706@cfl.rr.com
Subject: Re: [R-390] A bit more on my IF deck

It could be a difference in tube performance, but also keep in mind that there is
AGC on some grids and you could be seeing some residual AGC bias voltage.
Also, with the higher line voltages today (120+ VAC), the B+ lines will run
somewhat higher than spec. which could change the operating points of the

To compare against the voltages in the maintenance manual, I think you should
also be using the spec-ed AC line voltage input. A variac cranked down to 115
probably. Finally, these are very high impedance circuits. If you measure grid
voltage with a standard VOM, you could be dragging the voltage down through
the meter. Need to use a very high impedance VTVM like they had in the old
days for working with tube circuits.
Date: Tue, 07 Mar 2006 13:50:14 -0500
From: JMILLER1706@cfl.rr.com
Subject: Re: [R-390] A bit more on my IF deck

I just noted you are using a 410B VTVM which should be fine. So forget that part
of my comment. I can suggest no other reasons you are not getting -0.4... but
just be sure you are reproducing the exact test configuration the manual calls for.
Oh, another thing that can affect B+ voltage (and operating points) is a
conversion to solid state rectifiers, unless you have used a 220 ohm dropping
IF deck tips                                     page 240

Date: Tue, 7 Mar 2006 14:37:57 -0800
From: "Dennis Wade" <sacramento.cyclist@gmail.com>
Subject: Re: [R-390] A bit more on my IF deck

I am at somewhat of a disadvantage being at work with none of my diagrams,
but your problem sounds very much like the one I was having with my Moto IF
deck when I was trying to track down my AGC problems. Where I got to was a
leaky mechanical filter. I got there by lifting the ground side of the filter and
watching the resistance to ground go right back to where it needed to be. I
know its kind of vague at the moment..but when I get home I hope I can give
you more detail. But in the meantime, don't over look the possiblility of a leaky
filter(s). I ended up with two.
Date: 7 Mar 2006 23:15:42 -0000
From: "n4buq@knology.net" <n4buq@knology.net>
Subject: Re: [R-390] A bit more on my IF deck

><snip>...Where I got to was a leaky mechanical filter. ..............................

If you selected the "good" filter positions, did the resistance return to its correct
value? I see where the AGC line ties to the filters, so that is a good possibility.
Date: Wed, 8 Mar 2006 10:55:34 +1100
From: "bernie nicholson" <vk2abn@bigpond.net.au>
Subject: [R-390] leaky filters

 I also have seen quiet a few leaky filters, its caused by the foam packing inside
the filter becoming crumbly and sticky and mildly conductive, I have looked
inside a few filters and this seems to be something that will eventually happen to
all of them in time, The same problem is also happening in Kokasai filters, I have
removed the 2&4 KHZ filters in a couple of receivers and replaced them with
dedicated USB&LSB filters and crystal locked the bfo on 455KHZ with a built in
product detector {double triode in the ballast tube socket} it is a different receiver
altogether from the original , but when you switch off the BFO it reverts to the
original circuit for AM .
Date: Tue, 7 Mar 2006 22:22:12 -0600
From: "Barry" <n4buq@knology.net>
Subject: Re: [R-390] A bit more on my IF deck

Paydirt. I think I have some weak/gassy/whatever, tubes. I swapped V506
with another 5814 in the RF deck and I got about -0.1V at pin 2. I then swapped
it with one of the other 5814's in the IF deck. This tube yields about -0.5V on pin
2. I seem to recall that gassy tubes can cause low grid voltages, but not sure
about that. Also, it seems that the radio is a bit "hotter" with this tube
IF deck tips                                     page 241

I know Roger created a writeup on swapping tubes for maximum performance.
Maybe I'll give that a look-see. I didn't put these tubes on the tester before firing
this thing up. Maybe that will reveal something about them too (yes, I know the
*best* tube tester is the circuit itself, but I want to see if the Hickock will tell me
anything obvious). Oh well, this has been a fun exercise.
Date: Tue, 7 Mar 2006 21:24:52 -0800
From: "Dennis Wade" <sacramento.cyclist@gmail.com>
Subject: Re: [R-390] A bit more on my IF deck

Good news Barry. To answer your question, no..I had to actually lift the side of
the filter that was common, and not the switched side. Have a careful look at the
switching arrangement of the filters (if you care to now that your problem isn't
the filters apparently..good thing!). If you'd like the gory details let me know
and I'll have a look at the schematic and work it out again.
Date: Wed, 08 Mar 2006 08:46:36 -0500
From: Barry Hauser <barry@hausernet.com>
Subject: Re: [R-390] A bit more on my IF deck

Sorry .. I was going to post a reply on the missing -0.4 volt thing sooner, but
assumed you had already checked for grid emissions. Also, my knowledge is a
bit spotty in this area - I'm going mostly from what I've learned on this reflector
and I usually wait for someone more experienced to post a reply. So, someone
please correct/amplify on this in case I got it wrong: A tube may be good in
terms of no shorts and good quality, yet have a case of "grid emissions" - usually
synonomous with "gassy". In some sockets/functions, it may have little adverse
effect, however it was cited as one of the possible causes of fouled up AGC. As
far as I understand, tubes are not supposed to have anything emitting from the
grids at all -- they're inputs for control voltages. So, most likely, the gassy tube
was putting out an errant positive voltage, cancelling out the small negative
voltage you were supposed to be getting there. I magine, grid emissions could
be caused by internal defects in the mechanics of the tube, but (I think) are
mostly the result of the gas conducting some current out through the grid(s).
Practically all tube testers have a test mode for this. Some have dedicated setups
for testing grid emissions, others have a gas test. Some have a "gas" button and
you're supposed to press it during the quality test to see if there is any
movement of the meter. Others may have some kind of indicator bulb. There
was a thread way back where someone was having problems with AGC not
working and after a lot of checking of nearly everything else, found that it was
due to grid emissions from one of the tubes in the IF deck.                            Barry
IF deck tips                                     page 242

Date: Thu, 30 Mar 2006 13:33:41 -0800 (PST)
From: "Tom M." <courir26@yahoo.com>
Subject: [R-390] R-725 Schematic, TRD-15 notes, etc Here

I recently scanned some R-725 notes for an enterprising chap who wanted to
make his own. Like Archie Bunker would say, "I'd like to give this, what do ya
call, your wide insemination."The original schematic and notes from the TRD-15
manual are zipped up in parts here:


The notes on how to make your own R-725 IF deck are here:


Date: Thu, 6 Apr 2006 06:11:38 -0700 (PDT)
From: "Tom M." <courir26@yahoo.com>
Subject: [R-390] R-390 AGC Question, SLOW MED FAST

My 390 IF deck seems to have an AGC problem in that it has low AGC action on
FAST (when no timing capacitors are engaged) but good AGC on MED and
SLOW (when the timing caps are engaged). Anyone know what could cause
this? Seems counter intuitive. The old caps are good, the no-cap is bad?
Date: Thu, 6 Apr 2006 16:04:20 -0700
From: "David Wise" <David_Wise@Phoenix.com>
Subject: RE: [R-390] R-390 AGC Question, SLOW MED FAST

It's counterintuitive, as you said. The only thing that comes to mind is unlikely.
If C547 and C548 were both open, the AGC line would have next to no filtering,
and would vary with the envelope, reducing it to a small value. If you have a
scope, put it on the line. If nothing else, put on a high-impedance DC voltmeter
and tabulate voltage vs signal input.
Date: Thu, 06 Apr 2006 22:09:47 -0700
From: "Dan Merz" <mdmerz@verizon.net>
Subject: RE: [R-390] R-390 AGC Question, SLOW MED FAST

Tom, I assume you're dealing with 390 not 390a. There's C545 (0.1µfd) still
going from AGC line to ground when fast is switched in, shown in diagram I'm
looking at. If this is bad (open) then on the fast position there would be no
smoothing of AGC because I think this is the only smoothing capacitor to
ground in that position. When switching to med or slow the C546 and C547
caps, each 0.1 µfd, would be to ground or to the B+ and AGC would be
operative if they are good. My 390 has about the same level of AGC response
on fast and med on a strong AM signal but different response times, as expected
if it's working ok. The "no-cap" is actually one cap, C545, I think. I didn't track
IF deck tips                                     page 243

the circuit all the way to the controlled tubes on the AGC line. I see the 390A has
two of these 0.1µfd caps to ground on the AGC line. Dan.
Date: 27 Apr 2006 19:58:19 -0000
From: "n4buq@knology.net" <n4buq@knology.net>
Subject: [R-390] IF Transformer Covers

The IF deck alignment procedures call for transformer covers with holes in the
top to expose the slug drives. I really don't want to put holes in my permanent
covers. Anyone have a suggestion where I might find some spare covers I can
use for this? I figure the sizes used to be fairly common and available (old TV
radios and TVs, etc.), but not sure where I could find those now.
Date: Fri, 28 Apr 2006 09:17:10 -0400
From: "Tim Shoppa" <tshoppa@wmata.com>
Subject: Re: [R-390] IF Transformer Covers

390 or 390A? At least in my 390A either my covers already have the holes or I
can swap around with other cans which have the holes. A non-historically
accurate but easy "modern" way to make very good shields is to use modern
thin unetched PCB. Cut it with scissors, join it with a soldering gun, round it with
a file. I'm sure the purists who will never use a frequency counter or a scope to
align their 390 because they aren't mentioned in the Navy books will object, but
in terms of do-ability this has been the preferred method for decades.
Date: 28 Apr 2006 16:01:39 -0000
From: "n4buq@knology.net" <n4buq@knology.net>
Subject: Re: [R-390] IF Transformer Covers

It's an R390A. I don't have the measurements here, but perhaps I could get some
square aluminum tubing. It's available from McMaster but I don't know if I can
get an appropriate size. The PCB approach sounds good too. Thanks,
Date: Tue, 16 May 2006 11:37:13 EDT
From: DJED1@aol.com
Subject: [R-390] AVC voltages?

I've had a slight problem with my R-390A for awhile - the carrier meter reads
about 20 dB too high. I finally pulled the radio out of the cabinet last night and
did some diagnostics, but i need some sage advice from the group. First, I set the
IF gain according to the Rippel method (measure AF noise level), which also
gave me -7V at the diode load with 3 microvolts in. So that seems about right,
but still the problem existed. I measured the AVC at the back terminal strip: -12
V versus a nominal 9 V for 10,000 microvolts. This implies the AVC on the
controlled stages is not high enough. Measured with a 10 Meg voltmeter and a
URM-25. Then I measured the AVC voltage at all controlled tubes- With -12 V at
the AVC terminals on the back, the IF stages had -12 to -10.5 V on their grids,
but the mixers had -10.8 to -8.1 V , and the RF stage had -7.8V. I tried
substituting NOS tubes in the RF and worst mixer to see if the tubes were gassy,
IF deck tips                                     page 244

but no change. I then measured the resistance to ground of the AVC bus, and it
was about 500K as expected. Sooo- does anyone have data on AVC voltages at
the grids on a known good radio? If I had leaky caps pulling the AVC line
down, I would expect a much lower resistance reading. Any other suggestions?
The radio has not been recapped, but I'm reluctant to pull the RF module unless I
have some clear indication that that is the problem.                               Ed WB2LHI
Date: Tue, 16 May 2006 11:49:31 -0500
From: "Cecil Acuff" <chacuff@cableone.net>
Subject: Re: [R-390] AVC voltages?

It could easily be a cap problem. Many don't show leakage at the voltages
placed on them by ohm meters but will affect the operation of the circuitry at
their normal operating voltages. That's just a general statement about the caps
in most old tube radio's. With the antenna disconnected your carrier meter is
setting 20db above the zero or is it only 20db high with signal input? Does the
AGC switch still do it's normal thing when switching around between the
settings.....like the moment of silence etc.... Has the radio appeared to have lost
sensitivity or has it maybe only developed a problem with the metering circuit? I
would still expect the culprit to be a leaky paper cap or a resistor going way out
of spec. Both of which we know happens...
Date: Tue, 16 May 2006 16:16:23 EDT
From: DJED1@aol.com
Subject: Re: [R-390] AVC voltages?

Just to clarify- the radio works fine, and doesn't overload on strong signals. The
AVC seems to switch normally, and the meter zeros OK. However, the meter
pins with a signal input that should only read 80 dB. I haven't checked the
linearity, but I think it reads high for most of the range.                        Ed
Date: Tue, 16 May 2006 16:53:29 EDT
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] AVC voltages?

You could just have a problem with the meter set resistor R523. This is a 100 ohm
resistor across a 22 ohm resistor. This item has been a problem for setting the
carrier level meter since day one. Time has not improved the performance of the
circuit. The resistor gets dirty and hard to adjust. At low level low current the
meter lays at zero or near zero OK. But on a strong signal the circuit current
changes and in the dirty pot the conduction changes a whole bunch and the
meter reads high. Several fixes have been tried and are in use. A ten turn pot is
one fix. Just clean up the one you have is another fix. Add a few ohms in series
with the pot to move the adjustment spot off the worn spot is another fix. Then
you can replace the current pot.

As the meter circuit is not calibrated to any known standard, you can just live
with it. One way to set the pot is to set it to mid scale with a good signal coming
in. This is easier than trying to get the needle to lay at zero with no signal. Watch
IF deck tips                                    page 245

for some more post from others. Their are semantics on the WWW. One of the
fellows did a wonderful job of reading almost any point we could think of and
annotating the schematic with the voltages. That info is out there. I do not have
the address at hand or I would post it for you. If the receiver is working OK I
would think a problem in the meter circuit.                                         Roger AI4NI
Date: Wed, 17 May 2006 08:50:50 -0400
From: Miles Anderson <k2cby@optonline.net>
Subject: [R-390] AVC Voltages

I think we have two separate questions here.

(1) The actual voltage on the AVC line and
(2) the behavior of the carrier meter.

With respect to the AVC line, the most common problem (other than failing
tostrap the AGC-NOR terminals on the back panel) is a leaky bypass capacitor.
The AVC line is isolated at each controlled stage by a series 22k resistor and a
.005 bypass capacitor. It comes from a very high impedance source. Leakage in
any one of the bypass capacitors will drag down (closer to zero) the negative
bias on the whole line. This also means that you can accurately measure the AVC
voltage with a VTVM or other high impedance (1 meg or preferably 10 meg)
voltmeter. In checking for leakage, don't forget that the AVC bus also drives the
RF amplifier and is coupled through the bandswitch and the bandwidth control
that switches the IF filters. <snip>
Date: Wed, 17 May 2006 09:39:59 EDT
From: DJED1@aol.com
Subject: Re: [R-390] AVC Voltages

Thanks to all for the comments on my AVC problem. I disconnected the RF
chassis from the radio and found that the AVC line has a resistance to ground of
1.75 M, so something is leaky. The IF chassis shows more than 40 M, so it's OK.
Got some other strange results though. I put a DC voltage on the AVC line and
measured voltages at the test points in the RF chassis. Voltages were all in the
range of 10.5 V, versus 7 to 9 V with the same voltage on the AVC terminals. I
don't understand why the AVC voltage shoud behave any different than a DC
supply voltage, and the 5 V drop in AVC voltage can't be accounted for by a
1.75 M leakage current through a cap. Then I remembered the problem of the
antenna trimmer- it's hot with AVC voltage, and leaks when it gets dirty. I dug
up some alcohol and cleaned all around the gears, and watched the resistance
plummet to about 0.5 M. Must have been some water in the alcohol. I finally got
it all dried out and got the resistance back to where it started, but no better. The
strangest thing I found was that if I shunted the antenna trimmer to ground by
putting my fingers on it, the resistance at the RF amp test point increased, rather
than decreased?? Maybe I need an exorcism. Given that any further
investigation requires pulling the RF chassis, I've decided to defer that to next
winter when I think I'll recap the whole radio. For now, I'll have to live with
some minor errors in the meter readings. Ed
IF deck tips                                     page 246

Date: Thu, 18 May 2006 20:01:42 EDT
From: DJED1@aol.com
Subject: [R-390] AVC voltages revisited

Just a tidbit for anyone else who is investigating the AVC line: As I mentioned
before, I disconnected the cable to the RF module and made some resistance
measurements, which I thought indicated a leaky cap. As I was listening to the
radio last night, I was browsing through the Y2K manual (a great job). I was
surprised to see that the RF amp schematic was different than in my old TM, and
the differences accounted for the irregularities in resistance measurements.
Specifically, the newer manual shows a 1.5M resistor from the AVC line to
ground in the RF module, while the old TM shows no path to ground. Since the
new schematic agrees exactly with my resistance measurements, I assume I'm all
OK with the capacitors, and don't need to pull the RF deck.
Date: Thu, 18 May 2006 22:22:16 -0400
From: "Jim M." <jmiller1706@cfl.rr.com>
Subject: Re: [R-390] AVC voltages revisited

I have noted that if there is oil or conductive film residue on some tube sockets,
on some RF switch wafers (that carry AGC), or especially the insulated antenna
trimmer shaft, then the AGC control may tend to be degraded in the RF deck.
Over spraying RF deck switches or luibricating the antenna trimmer shaft can
cause this. The residue can be removed by "Big Bath" or equivalent moisture
displacement spray. Leaky AGC line bypass caps can also be suspect. It's a high
impedance circuit so it doesnt take much.
Date: Mon, 17 Jul 2006 17:31:40 -0400
From: shoppa_r390a@trailing-edge.com (Tim Shoppa)
Subject: Re: [R-390] R390 whistle filter data

>In Chuck Felton's r390 article in Electric Radio he showed the addition of a 5Kc
>whistle filter using a 1 Henry choke and IIRC 690 µF cap in series.

My calculations do NOT put this filter at 5kc, but at 6.061kc. Of course winding or
stray capacitance might bring the resonant frequency down to 5kc.

>Three questions. Was that a mis-print for the inductor value? If not does
>anyone know what he used for the inductor? Has anyone tried the mod?

Audio filters using L's and C's tend to use inductors in the 100mH to 1H range.
The "classic" surplus example is the 88mH telco line-loading toroid popular in
every single RTTY decoder for many decades. I think there were Brit and Euro
equivalents at slightly different values. Some very small filament transformers
might exhibit a winding inductance in the 1H range if you want to play around
(although most will be larger). Hammond sells iron-core chokes in this range
(well, generally larger, but I think they go down to 1H) new today. For AM
reception on crowded SW bands I find the 8kc filter width does a pretty good
IF deck tips                                     page 247

(but not perfect) job of getting rid of a carrier 5kc away. Tune a little away from
the QRM and it does even better (even if introducing some distortion, it still is
slightly better than switching to the 4kc IF bandwidth.) I can see how 6kc filters
became a "standard" on crowded bands!
Date: Mon, 17 Jul 2006 21:25:48 -0700
From: John Kolb <jlkolb@jlkolb.cts.com>
Subject: Re: [R-390] R390 whistle filter data

I once made a very effective one from a 88 mH toroid (telco loading coil) and the
appropriate sized capacitor. 88 mH coils aren't as common as they once were but
still many floating around.
Date: Fri, 21 Jul 2006 08:45:19 -0700
From: "James A. (Andy) Moorer" <jamminpower@earthlink.net>
Subject: Re: [R-390] Wanted: non-A IF decks

I have a bunch of them, and other R-390 (and R-390A) parts. Being 50+ years old,
they are in various states of aging. Most of them look like they can be restored.
$75 each for restorable ones (plus shipping).

They come without tubes or tube shields but with the BFO coil. Also have power
supplies ($45 ea - but HEAVY), audio modules ($45 ea - also heavy), PTO ($75),
some restorable front panels ($75 ea) and various RF deck parts.
Date: Fri, 21 Jul 2006 14:49:41 -0400
From: "Drew Papanek" <drewmaster813@hotmail.com>
Subject: [R-390] R-390 IF Module (was: Wanted)

Some years ago I worked on a 75A-3 for a friend and I noted that it had only the
SSB filter and that the other filter switch position had no filter plugged into its
corresponding socket. On a whim, I inserted a cap (for coupling) and a couple of
resistors (one for plate load, the other for grid bias) into the unused filter socket.
I then noted that reception in the now-enabled second filter switch position had
quite good audio, if a bit broad.

I've pondered a modification for the R-390A along somewhat similar lines. The
16 KC filter would be bypassed and the q-spoiler resistors in the IF cans would
be increased in value or perhaps eliminated entirely so that the IF cans alone
would determine the radio's bandwidth in the 16KC position.

The IF would be realigned to provide a bandwidth for good audio quality and
would not affect operation with the other filters since its bandwidth would be
wider than those of the other filters.

The IF module so modified would have higher gain than original, particularly in
the 16 KC position (no filter insertion loss) and that would need to be
compensated for. Perhaps the modification could incorporate a switching
IF deck tips                                    page 248

arrangement to alter the cathode bias resistor on just the first stage or maybe
also on subsequent stages.

Another although somewhat inferior gain compensation arrangement would
just replace the 16KC filter with an attenuator to compensate for the now-
missing insertion loss, and the IF gain pot would be reset. (The Q-spoiler
mod/realignment would also be done.)

Just my thoughts on conserving the diwndling supplies of non-A IF modules
while helping to insure that the comparatively plentiful -A IF modules get
irreparably hacked.
Date: Thu, 3 Aug 2006 21:55:35 EDT
From: ToddRoberts2001@aol.com
Subject: Re: [R-390] flying R390A

Ken, I found the 500KHz filters from the 51J-4 work nicely in the R-648/ARR-41.
The stock filters of 1.4KHz and 6.0KHz are not the best choices. The 6.0KHz is
fine for AM but the 1.4KHz seems too wide for CW and really too narrow for
SSB or AM. The F500J31 is a good substitute for the 1.4 - just about right for SSB
and narrow AM. I removed the 2 original filters and installed HC6-U size crystal
sockets in the I.F. module chassis where the original filter pins would go. The
ends of the solder-type filter terminals on the original hard-wired F500F14 and
F500F60 can be snipped off and the filters will then plug into the crystal sockets
just like the filters do in the 51J-4. I subbed a F500J31 for the 1.4 and plugged in
the F500F60 for wider BW and the radio really works well with those 2 selectivity
choices. And it is easy to just plug in the slightly-modified F500F14 back into the
radio if that filter is wanted again instead of the 3.1. 73 Todd WD4NGG
From: On Behalf Of William G Feldmann
Sent: Wednesday, August 16, 2006 01:20 PM
Subject: Re: [R-390] R-390 (Non A) Problems

I would also check on some other bands using different front end coils like below
8mc and above 16mc just to eliminate any possible problem in the front end coils
or transformers. If a front end transformer is bad it's most likely a bad SM cap
but I've only worked on the A model's transformers that are a snap to remove
and fix. Hopefully the non-A ones can be removed by just pulling the slug racks
and removing a small screw in the center of the coil like on the A. But don't
know, never had any problems with them in my non-A.

Also check the AGC is working by looking at the AGC line voltage and being
sure the receiver seems to not be overloading on strong signals. If the AGC is
working OK and the RF stages are OK, then you most likely have a problem in
the carrier meter circuit.

Try and see if there is a difference between meter reading on the same signal
when switching between MED and SLOW AGC. If there is a meter level
difference the 2uf oil filled cap on the plate of the meter amp in SLOW is most
IF deck tips                                     page 249

likely leaking. It's C551 in a A model but will be a different reference number on
the non-A model.

If the AGC is working it's most likely a cap or resistor that's failed in that meter
amp circuit.

Also be sure the carrier meter just isn't pinned below zero. That meter zeroing
pot trouble some and is very hard to adjust. I usually replace it with a ten turn
one. I'll mention that in my part 2 article in the Sep. issue of ER. Hopefully
nothing has damaged the meter because stock ones are very hard to fine thanks
to the demil process most have gone through.

Anyway the problem is most likely in the IF module that's easy to pull and run
out of the radio. On my A model I could lay it on its side on a piece of wood on
top of the radio and still connect the cables for testing as I mentioned in my
article in the Aug issue of ER. I think you should be able to do that on a non-A. I
have a Collins non-A R-390 that hasn't had any problems besides a few weak
tubes. But I sure went through hell with bad SM caps in the front end of my
Stewart Warner R-390A that I talked about in my part 1 ER article. I'm at my
second house in Mammoth Lakes but when I get back to Palmdale I'll look some
more at the manual for my non-A for some ideas if your still having trouble. Let
us know how you are doing.
Date: Mon, 28 Aug 2006 22:32:54 -0500
From: "Patrick J. Jankowiak" <recycler@swbell.net>
Subject: Re: [R-390] Repairing broken trimmer capacitors, search

how to repair small air-viarable capacitors:
Date: Fri, 8 Sep 2006 16:31:42 -0500
From: Tom Norris <r390a@bellsouth.net>
Subject: Re: [R-390] Krohn Hite 3200

> G'day group. I just purchased a Krohn Hite 3200 dual
> filter which I intend to use as a bandpass filter or
> as a notch filter with my R-390A. Originally I was
> going to use it on the audio output to speaker but
> when I got it, I discovered it has a 100K input/output

I suppose you could drive it from the diode load with its output feeding the
audio deck. You may end up trying several different ways to see which works
best. It shouldn't have any problem with the signal level coming from the diode
load, since the input limit is 4.5 volts for both the 3200 and 3202. I've not used the
filter with any equipment, but I've calibrated a few dozen of them at work, they
can be fairly forgiving impedancewise, give it a try between diode load and the
audio deck first off.
IF deck tips                                     page 250

But... if you have a dual 3200, then you have a 3202, there are several ways to use
it for a notch/bandpass filter and the thing should work fine at IF frequencies as
well as audio. I think it's good to 2Mhz in high/low pass. In fact it might even
be easier to use at IF freqs. If you were to use it on the 455 Khz IF freq, you'd
just leave it on the x10k scale and tune around for the notches. To use it for
audio you'd end up having to switch between the x10 and x100 positions, bands
2 and 3 IIRC and unless you were just going to set it up for a single notch freq
and leave it, it would drive you batty running back and forth setting it up each
time. You might want to refresh my memory, or hopefully someone else is
more familiar with this than I am.
Date: Sun, 10 Sep 2006 11:35:04 EDT
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] oscillation in my R-390 IF

Have you had a chance to get out the nut drive, small wrench and Philips screw
drive to massage all the hardware in the IF deck? A lot of problems arise from
loose and corroded hardware points. These are old receivers and your R390 is
older than the R390/A. Not a sure fire cure but a place to start. Also get the bolts
that mount the tube sockets. My R390 TM is still packed in moving cartons from
July 2004 so I do not have it for reference. As the R390 filaments are in series you
just cannot unplug a tube and divide the deck into neat sections to divide the
problem down. The IF cans have a bunch of solder joins in them. You can get the
covers off and do an eye ball and remelt of the solder points. You are just going
to find a sorry solder joint some place that is a high impedance point. You likely
cannot find it with an ohm meter as the point will measure under an ohm with a
meter and be open at 455Khz. Some point should be filtered by a cap. The point
is not getting the filtering it needs because of a solder joint. That point radiates
some signal around under the deck and it feeds back to oscillate.

Does changing the band width switch give you any clues?
Not an easy problem to resolve.
Date: 11 Sep 2006 13:29:54 -0000
From: "n4buq@knology.net" <n4buq@knology.net>
Subject: [R-390] IF Gain Problem

I'm having some "strange?" problems with the IF gain in my R390A. If I crank it
too far CCW (towards max gain) the radio will suddenly go silent and the diode
load reading will spike. In order to get the radio to play again, I have to turn the
control to about 1/2 position and then increase it back to a more normal setting.

Any ideas what's causing this? It occurrs whether in MGC or AGC mode and
can be triggered by a strong signal on the antenna input or switching the
bandwith position. Switching the BFO on and off will also sometimes bring the
radio back but sometimes it won't and I have to resort to backing down on the
IF gain to get it working again.
IF deck tips                                     page 251

I know the IF gain doesn't need to be too "hot" and I can actually run the radio
with the IF gain at about 50% and it works fine, but I'm wondering if this
"swamping" effect is seen in other radios? I need to align the IF deck properly
and set the IF gain control properly, but am thinking I might have issues with
this deck.

I've recapped it and replaced an resistor or two that were high but haven't found
anything else that seemed off with it. Thanks, Barry - N4BUQ
Date: 12 Sep 2006 14:32:09 -0000
From: "n4buq@knology.net" <n4buq@knology.net>
Subject: [R-390] IF Deck Problems Revisited

As reported earlier, when I increase the IF gain past a certain point, the diode
load voltage spikes to about 90 volts and the radio goes silent. As Roy
suggested, I checked the IF output and, sure enough, the thing was going into
self oscillation. The frequency counter indicated it was about 410kc.

I pulled the IF deck and checked for loose grounds and bad solder joints and
didn't find anything that I would suspect as a problem. I put the deck back in
place and the problem persisted. I began pulling tubes trying to isolate the
problem. With only three tubes left in the deck and still seeing the problem, I
figured I had it pretty much narrowed down and would pull the deck again and
look closer in those areas.

All this time, I was running without the IF can covers in place. I don't have holes
in the tops of the cans and had been tinkering with the adjustments with them
off. I put the can covers back on and it appears that the problem has mostly

I suppose a combination of the IF cans being pretty far out of adjustment and the
can covers removed was allowing the signals in the coils to interact with other
components and provide a feedback route. Not sure about all that but it does
seem to have cured the problem. I think once I get the holes in the cans, get
them properly secured, and do the complete IF alignment, this "problem" will no
longer exist.

Thanks for all the input. While my "problem" was probably more just stupidity
than anything else, it did help me figure out what was going on.
Date: Tue, 12 Sep 2006 16:17:40 -0400
From: "David C. Hallam" <dhallam@rapidsys.com>
Subject: RE: [R-390] IF Deck Problems Revisited

I, too, just solved my R-390 IF deck oscillation problem of a different sort. I
followed the procedure outlined yesterday by Roger, AI4NI, to set the crystal
filter, Z501. I had been using the procedure given in the manual to set the crystal
filter trimmer null, then could not peak the 1KC coil, and the deck would go into
oscillation. I must have been doing something wrong.
IF deck tips                                     page 252

Following Roger's suggestion of setting the signal generator to 455.00KC with
the frequency counter and to set the trimmer for null there, I found the null of
the 0.1 pass band came at a significantly different point in the trimmer's rotation
than I had set before, about 60° and now I could peak the 1KC pass band coil.
The oscillation was gone. Now maybe I can get on with solving the AGC
Date: Tue, 12 Sep 2006 19:00:32 EDT
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] IF Deck Problems Revisited

So I am like reading in my 1977 ARRL handbook in the VHF section. And I come
across this subject of lead length and caps forming resonant circuits. The book
subject was how much cap and how much lead makes a resonant circuit at like
144 MHZ. The point that comes to mine is that an inch of wire and a by pass cap
gets resonant at 455 (OK so 410 in your deck). Where do we get a wire and cap
to resonate in an R390 or its new replacement? One each bad solder joint or 50
year old poor mechanical connection on a ground point.

So a poor connection on a ground point leaves a cap and its wire hanging like an
antenna to some point. Then to really mess with us it behaves like a resonant
circuit and injects the most unwanted signal back into the deck some where.

I think you are on it with getting the IF can covers back on. If you do not have
holes in the can tops, drill only one can and move it around as needed. Keep the
other ones covered. The nuts do not need to be installed but drop the covers on.
When you are done leave the can with hole on the AGC transformer.

Running with the covers off may be a self inflicted curse.
Date: Tue, 12 Sep 2006 23:37:29 -0400
From: 2002tii <bmw2002tii@nerdshack.com>
Subject: Re: [R-390] IF Deck Problems Revisited

> The point that comes to mine is that an inch of wire and a by pass cap
> gets resonant at 455 (OK so 410 in your deck).

It would have to be an awfully large bypass capacitor. Small wire has a high
frequency inductance of about 20 nH per inch, so with typical bypass values of .1
uF to .01 uF the resonant frequency will be 3-10 MHz. To get it down to 455 kHz,
you would need about 8 uF. (This is the very reason that you don't see values
much above 0.1 uF used as bypass caps at HF, and even smaller at VHF. Along
with very short leads. A 50 pF cap standing up on 1/2" leads resonates at around
150 MHz.) See <http://www.ee.scu.edu/eefac/healy/indwire.html> for
formulae to
calculate the inductance of a straight wire.

> So a poor connection on a ground point leaves a cap and its wire
IF deck tips                                     page 253

> hanging like an antenna to some point.<snip>

A series LC is a low-impedance, high-current circuit element. If the nether end is
disconnected, it can't draw any current, so it isn't an efficient radiator. Now, a
bad ground could cause the capacitor to quit bypassing, which could easily cause
oscillation. But in this case, it was probably the unshielded IF's.
Date: 14 Sep 2006 14:03:48 -0000
From: "n4buq@knology.net" <n4buq@knology.net>
Subject: [R-390] Staggertuned IF Question

Are all IF modules capable of stagger-tuning? I started trying this with my
current project with no results. The IF won't even think about hearing a 467kc
signal. I was able to do this on my Motorola, but not this one. I seem to recall
reading where not all IF modules were designed to accomodate stagger-tuning.
Is this true? If not, then I suppose I have more work to do. If so, then do I
assume I peak all the slugs for 455kc?
Date: Thu, 14 Sep 2006 11:19:52 -0400
From: Roy Morgan <roy.morgan@nist.gov>
Subject: Re: [R-390] Staggertuned IF Question

Certainly, it just depends on how staggered you try to make it. With the
development of 30 mc IF amplifiers for radar systems in WW-II, there came a lot
of study of the stagger tuning of rf/if amplifiers. Text books of the era contain
the theory and practical methods for arriving at flat passband response. This
depends on setting the Q of the tuned circuits, the mutual coupling values, and
separation of tuning points, as I remember.

Imagine a strip tuned to one frequency. It will have the well understood bell
curve pass band shape. It the Q of the coils and their coupling coefficients will
determine the shape of the transfer characteristic. If you now tune some of the
circuits slightly above and below the center, the top of the curve will broaden. If
you tune them farther and farther away from center, you can imagine a double
or triple hump characteristic. Getting the whole mess to be very flat depends on
the Q of each circuit, the coupling amounts, and the degree of departure in
tuning frequency from the center.

>... The IF won't even think about hearing a 467kc signal....................

We can assume this is an R-390/URR (the "Non-A"). Notice that T-501 and T-506
have resistances across the primary and secondary of the transformer,
respectively. All the IF transformers also use multiple windings in a "feedback"
arrangement to arrive at various selectivities. The IF transformers are pretty
complicated, and were made with carefully engineered coupling coefficients to
make this all work out right.

>I...........where not all IF modules were designed to accomodate stagger-tuning.
IF deck tips                                   page 254

It well may be, but this is the first I've heard of it.

> If not, ..........I peak all the slugs for 455kc?....................

If you can arrange a sweep generator/detector system to do your tuning, you
will be able to see the effect of your tuning experiments. An Army publication
ST 32-152.pdf, entitled "Visual Alignment of Radio Receivers R-390/URR and R-
390A/URR" is a good place to start. Go to: http://www.r-390a.net/ and look
under References, in the Army section. (It describes sweepers that do not have
retrace blanking, so adaptation of the methods is needed for more modern
equipment.) There have been articles published on how to build sweep
generators. I don't know if FAR Circuits has such a board/article available, but
someone should check their web site and report. But plenty good enough sweep
generators are available on the surplus market. These topics of stagger tuned IF
strips and sweep alignment methods are both very interesting to me, though I
have not yet done very much experimenting. When my Radio Emporium is set
up at my new QTH, I certainly will.
Date: Thu, 14 Sep 2006 10:46:45 -0500
From: "Cecil Acuff" <chacuff@cableone.net>
Subject: Re: [R-390] Staggertuned IF Question

I'm working from memory here so YMMV....(your memory may vary) My
thoughts are NO. As I remember there is a capacitor involved on each can that
sets the Q for the coil...I can't remember if the cap needs to be there when you
are to stagger tune or vice versa.... Seems the cap reduces the Q allowing a
smooth bandpass when stagger tuned where without the cap it's too peaky....
Roger you will have to fill in the blanks on my memory cell issue on this one...
I know the R-390/URR is straight tuned but I've heard the "A's" are split...some
setup for stagger tuning, some not. I've heard also of folks cutting out the caps
and straight tuning but I'm not sure there are not stage gain problems with
doing that... Good subject though...
Date: Thu, 14 Sep 2006 13:05:08 -0400
From: <kirklandb@sympatico.ca>
Subject: Re: Re: [R-390] Staggertuned IF Question

CAPs generally change the resonant point not the Q of the circuit. Q is a measure
of the energy loss in the tuned circuit. As you load a parallel (or series) tuned
circuit down, you lower the Q. For parallel tuned circuits, decreasing the parallel
resistance lowers the Q. The Q of a parallel tuned circuit is affected by both the Q
of the inductor and the capacitor. Generally the Q of the inductor dominates -
inpart due to the resistance of the wires.
IF deck tips                                     page 255

Date: 14 Sep 2006 18:09:07 -0000
From: "n4buq@knology.net" <n4buq@knology.net>
Subject: [R-390] Re: Staggertuned IF Question

I notice the values for the caps and resistors in the cans aren't specified except to
say they are part of the transformer. I wonder if these components could be the
culprits here? They sure look like a pain to replace, but could do that if
necessary. I peeked at them during my lunch break and if I could see them well
enough, I noticed that some of the caps are the rectangular molded variety while
the others appear to be dipped silver micas. I wonder if the differences
were due to their capacitance values or if SMs were better on the input or output
and the others were better in their respective posions. If I did replace these, I
assume I'd use SMs in both positions but was curious.
Date: Thu, 14 Sep 2006 11:16:24 -0700
From: "David Wise" <David_Wise@Phoenix.com>
Subject: RE: [R-390] Re: Staggertuned IF Question

Silver mica's were a later development which superseded the molded ones.
Production overlapped for quite a while, moreso for some values than others,
with a lot of variation between manufacturers. Cost was undoubtedly a factor
too. I wouldn't be surprised to see a mix. For our purposes today, SM's are
superior in all respects.
Date: Thu, 14 Sep 2006 14:30:22 -0400
From: Roy Morgan <roy.morgan@nist.gov>
Subject: Re: [R-390] Staggertuned IF Question

I seem to remember that the R-390A has resistors in each can that are the "Q
spoilers". A capacitor is normally of such low loss that it will not affect the Q by
much. One (BAD) modification was to cut out the resistors in the -A IF cans to
get extra gain.. your receiver got real "HOT". Trouble is, the IF bandpass went to
hell, and there was too much gain. NOT a good modification.
Date: Thu, 14 Sep 2006 15:05:46 -0400
From: Mark Huss <mhuss1@bellatlantic.net>
Subject: [R-390] Staggertuned IF Question

I seem to remember that the first run of R-390A (the ones WITHOUT the
trimmers on the top of the mechanical IF Filters. The mechanical filter cover does
not have a dimple at the mounting screw) was straght tuned. When Collins did
the mod to add the trimmers, they also changed the circuits on the IF
transformers to stagger-tune them. At least that is what I remember from the R-
390A classes.
IF deck tips                                     page 256

Date: 14 Sep 2006 19:22:08 -0000
From: "n4buq@knology.net" <n4buq@knology.net>
Subject: Re: [R-390] Staggertuned IF Question

This one has trimmers on both ends of the filters and it has RC across the L in the
transformers so I assume this one is broadband. I think I have other issues with
it, though. I tried Roger's method of removing the 3rd mixer and injecting 455kc
at the plate pin. It took a LOT of signal to be able to hear it through the IF deck.
The crystal's trimmer and xfmr don't seem to peak like they should and it reqires
me to crank the slugs in T501 and T502 to the near limits to get them to peak.
Switching to AGC automatically gets me 20dB on the carrier level meter as
opposed to zero in MGC. I'm pretty sure I have work to do...
Date: Thu, 14 Sep 2006 15:23:41 -0500
From: "Cecil Acuff" <chacuff@cableone.net>
Subject: Re: [R-390] Staggertuned IF Question

Well I said I couldn't depend on my memory of this.....My technical side said
resistors but my memory for some reason had caps stuck in it. Roy's comments
about removing the resistors rings the bell for me...that was what I had heard...
don't remove whatever component it was because it screws up the stage gain
balance making the IF deck too hot by increasing the Q of each stage.... Memory
is a great thing...just not always accurate as I have proven.... That still doesn't
speak to the fact that some "A" radio's were stagger tuned and others were
not.....at least that is what I have been told.
Date: Thu, 14 Sep 2006 16:48:03 -0400
From: Bill Cotter <n4alg@qx.net>
Subject: [R-390] Staggertuned IF Question: Visual Alignment Doc

Does anyone have this Army document available in pfd format to share? It
might be a good document to place in the common access web pages.
Date: Thu, 14 Sep 2006 16:56:30 -0400
From: Mark Huss <mhuss1@bellatlantic.net>
Subject: Re: [R-390] Staggertuned IF Question: Visual Alignment Doc

See http://www.r-390a.net/ and search for ST 32-152
Date: Thu, 14 Sep 2006 14:11:25 -0700
From: "Kenneth G. Gordon" <kgordon2006@verizon.net>
Subject: [R-390] Re: Visual Alignment Doc - ST 32-152.pdf

I have that. I'll post it to a web site tonight and let the list know. However, it is
not the most up-to-date way of doing visual alignment.
IF deck tips                                     page 257

Date: 15 Sep 2006 18:32:53 -0000
From: "n4buq@knology.net" <n4buq@knology.net>
Subject: [R-390] IF Deck Revisited (Revisited)

Since I'm having several issues with the IF deck, I made a geniune effort to check
resistances and voltages on all tube pins in the IF deck. This time, I recorded all
the findings along with their spec'd values so I can refer to that list for places to
check. Most things were fine, but there are some grids with positive values
where they should be negative, etc., so I'll begin there. The first thing will most
likely be to try new/different tubes in some of those positions as I assume grid
emmissions could be a problem for symptoms like that. One problem I'm having
is when I switch from MGC to AGC, the carrier-level meter jumps up 20dB and
stays there. I found the cathode resistor on V506A (R548) to be about 41-ohms
instead of 27. I don't have a replacement, but I put a 100-ohm resistor in parallel
which should bring it down to about 28 ohms. The carrier-level meter jumped
up somewhat in MGC, but I can re-zero it and when I switch to AGC, it still
jumps up 20dB so all I did was change the reference point. Not the main
problem... What I'm wondering is a good way to debug this thing. Is it possible
to start at the input and work my way forward (or vice-versa) and try to get it
working properly stage-by-stage?
Date: Fri, 15 Sep 2006 15:20:25 -0400
From: Barry Hauser <barry@hausernet.com>
Subject: Re: [R-390] IF Deck Revisited (Revisited)

I don't know if this could be it, but you should check the tubes for grid emissions
on a tube tester, as well as transconductance. Some testers have a grid emissions
check setting, but on others it's (I believe) synonomous with the gas test. You
can try swapping in new tubes, but if your spares came from the same batch,
they may be similarly afflicted.
Date: Fri, 15 Sep 2006 15:42:19 -0400
From: "Tim Shoppa" <tshoppa@wmata.com>
Subject: [R-390] AGC action on oscillator frequencies, cures?

I usually use my 390A to listen to (surprise!) AM SW and BCB broadcasts. And
when I do use it for CW, I usually turn off AGC (unless I am in fear of my
eardrums being broken!). But sometimes I turn on the BFO and use it with AGC,
and it's obvious that oscillator frequencies are shifting about (hundreds of Hz)
under strong AGC action. The 17MHz oscillator (below 8Mc bands) seems to do
the most shifting. This has been discussed here before, and the concensus seems
to have been that AGC action on the mixer tubes causes varying loading on the
oscillator, but have any cures/mods ever been propsed/discussed/shot down?
IF deck tips                                     page 258

Date: Fri, 15 Sep 2006 15:48:52 -0400
From: "David C. Hallam" <dhallam@rapidsys.com>
Subject: RE: [R-390] AGC action on oscillator frequencies, cures?

Get a copy of Electric Radio for October 2005 and look at the article by Ron
Deeter. See if that does anything for you.
Date: Fri, 15 Sep 2006 20:00:43 EDT
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] Staggertuned IF Question

>... seem to remember that the first run of R-390A (the ones WITHOUT the
trimmers on the top of the mechanical IF Filters. The Mechanical filter
cover does not have a dimple at the mounting screw) was straght tuned.
When Collins did the mod to add the trimmers, they also changed the
circuits on the IF Transformers to stagger-tune them. At least that is
what I remember from the R-390A classes.
I think you are right on the Collins Radios. Then later non Collins manufactures
went back to the straight 455 tuned IF strips. The transformer and cap values in
the cans were changed to get enough bandwidth and can so that a straight tune
was wider than the mechanical filters. As most of the receivers were not Collins
receivers most of the R390/A are straight tuned. We tuned every thing straight.
Remember I was tuning for a bunch of CW operators and they could have cared
less about any thing more than 2K wide. If you are trying to tune the IF for
some good Short Wave AM reception, then getting the sweep generator out and
doing the adjustment with a visual pattern on the scope is the way to go.

Try stagger tuning your IF deck and it will not take you long to determine if it is
a stagger tuned deck or not. More bandwidth is more fidelity. It is also more
noise in the band pass. If you are doing DX SW a narrow bandpass may still be a
better option. You can get a lot more fidelity by recapping the AF deck up to a
good 16KHz audio than you realize by opening up the IF bandpass. Until you
get the Audio deck to respond to 16KHz there is little point in trying to tune an
IF deck out to that response width.
Date: Fri, 15 Sep 2006 20:10:39 EDT
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] Staggertuned IF Question

>........... I tried Roger's method of removing the 3rd mixer and injecting 455kc at
the plate pin. It took a LOT of signal to be able to hear it through the IF deck.
The crystal's trimmer and xfmr don't seem to peak like they should and it reqires
me to crank the slugs in T501 and T502 to the near limits to get them to peak.
Switching to AGC automatically gets me 20dB on the carrier level meter as
opposed to zero in MGC. I'm pretty sure I have work to do...
IF deck tips                                     page 259

Barry, this does not sound good (Pun Intended). Time to look at the crystal and
the signal generator and freq counter. You may check the coupling cap you use
for injection. It reads as if your frequency is off some where. T501 and T502
should not change peak when you move back up the circuit chain and still inject
455. Why AGC gives you more than MGC I have no idea. That sounds like a
problem of its own. We always expect that AGC has the gain off ground and
thus less than MGC.
Date: Fri, 15 Sep 2006 20:40:18 EDT
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] IF Deck Revisited (Revisited)

You wrote that the problem persisted in the IF deck as you injected 455 into the
plate of the third mixer. You can leave the RF deck aside for a bit.

Next do a wire harness check on the RF gain and from the rear panel to the IF
deck. Lay the receiver on end and swing the IF deck out. Do the harness
measurements from somewhere out side into some where inside the IF deck to
ensure you are not going through a bad pin in the IF deck connector.

Check the receiver in all the KC bandwidths on the IF deck. A likely problem is
in a mechanical filter circuit and AGC circuit at the mechanical filters. A couple of
the bandwidth switches get the filters and AGC circuit combined.

An open in the AGC line will get you. In MGC there is a big resistor to ground in
the IF deck. It is good enough to give you MGC operation even with the jumper
on the back terminal board open. Check that jumper for a loose screw. When
you go over to AGC you expect a negative voltage on the AGC line instead of
ground. IF the AGC is open then you get a more positive grid voltage instead of
a negative grid voltage. So you get more gain in AGC than in MGC while we
expect less gain.
Date: Fri, 15 Sep 2006 21:01:15 EDT
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] AGC action on oscillator frequencies, cures?

I have on sure cures. One problem is current limiting through the deck
connectors. But once you deox them and check the back side for good solder to
ensure good cross section for current conduction there is little you can do to
enhance the current path in these elements. But if you have real bad pull, it could
be worth your time to do an inspection and repair if necessary.
These receivers did shift. But most operators though of them as very stable. Like
they never had an opportunity to work with a better receiver as one had not
been built back then. But if yours shifts enough to be noticeable you likely have a
problem worth investigating. It sure would be nice if you have two receivers to
set up side by side to determine if one shifted more than the other. Many trouble
calls went down as no trouble found when we did side by side test of two
receiver and found the difference to be antenna choice or just a bad ear night.
Fifty plus years of age makes a difference. A guy in San Francisco area makes
IF deck tips                                    page 260

solid state replacements for tubes. He could make you up some solid state tubes.
You use the screen voltage pin into a zener diode regulated voltage. The cathode
becomes the FET base. You decouple the cathode resistor back to ground by
selecting the correct filament pin. You add to the cathode resistor to get the grid
bias to fit the base bias voltage you need. A resistor into the screen zener
regulated voltage becomes the cathode or drain load. A cap couples the signal
back to the plate and the plate voltage is ignored. He puts the stuff in a nice
sleeve with a 7 pin socket. Noise is lower. You can reengineer the guts for more
or less gain. The filament voltage heat goes away. You never have to check the
tube again. I have a nice 6DC6 in one of my R390/A. The noise of the RF tube is
not the limiting factor in getting a better signal to noise ratio out of my receiver.
So until I get to the source of my noise problem, more solid state tubes are not of
value to me. I like my one solid state replacement. It is canned. I know not what
is inside. It performs a little better than any 6DC6 I own. I do not think it
performs better any 6DC6 that I could own. I have not measured it to be sure.
So there are things that can be done.
Date: Sat, 16 Sep 2006 09:22:49 -0400
From: Mark Huss <mhuss1@bellatlantic.net>
Subject: Re: [R-390] Staggertuned IF Question

As I was taught (1975) at Devens (ASA), you tune using the Visual Alignment
and stagger tune flat on 16 kHz bandwidth. As an aside, it was mentioned that if
you ran across an IF deck with a filter cover with no dimple, tune that one
straght. No mention of replacing the IF Deck with the newer ones. Making it
meet spec was a big deal, since you did not know where it might be four years
down the road. For 'Hogs' and 'RATT's' ( Morse Code Intercept and Radio
Teletype) you could get a better noise floor by straght tuning them, and we did
that on special order, and made a notation with grease pencil on the IF Deck's
filter cover.R-390's and R-725's required sweep alignment for best operation.
Never bothered to do the three-point alignment on them (mostly R-725s).
Besides, the point on them was to get flat phase shift through the IF deck, with
bandwidth being secondary. They were used for doppler DF, and phase shift
could throw them off a few degrees, as well as widen the propeller, making
direction more ambigous.
Date: Sat, 16 Sep 2006 09:52:29 -0500
From: "Cecil Acuff" <chacuff@cableone.net>
Subject: Re: [R-390] Staggertuned IF Question

Good stuff....that's what I was looking for. Some way to know when to do what.
Sounds like one can stagger tune or straight tune the dimpled cover decks...your
choice depending on how you will use the radio but always straight tune the
decks without the dimple. This probably needs to go into the Y2K book
somewhere....and Pearls.
IF deck tips                                     page 261

Date: Sat, 16 Sep 2006 10:22:17 -0500
From: "Barry" <n4buq@knology.net>
Subject: Re: [R-390] Staggertuned IF Question

Is it possible to switch filter covers between a straight-tuned deck and a stagger-
tuned deck?
Date: Sat, 16 Sep 2006 13:07:55 -0500
From: "Barry" <n4buq@knology.net>
Subject: [R-390] IF Resistance/Voltage Chart

I mentioned I had documented the resistance and voltage readings for the IF
deck I'm working on. I created a WordPad document and placed it here:
Some of the values jump out at me as potential problems (e.g. grid voltages
positive when they should be negative, etc.), but some of them are more subtle.
If you do open the document and see anything that you care to comment on, by
all means let me know. I'm trying to get this thing working right.
Date: Sat, 16 Sep 2006 18:26:34 EDT
From: ToddRoberts2001@aol.com
Subject: Re: [R-390] R-390 IF - Z501

If the Z501 adjusting screw top was broken off when it was in the correct
position it should still work just fine. I think the adjustment screw setting is not
too critical even if it is off slightly. Trying to repair or salvage Z501 with a broken
off adjusting screw is going to be tough. I think Fair Radio has the Z501 IF
transformer for $9.50. 73 Todd WD4NGG
Date: Sat, 16 Sep 2006 17:53:41 -0700
From: John Kolb <jlkolb@jlkolb.cts.com>
Subject: Re: [R-390] BFO Turns Counter (was RE: Spinner knob for R390

Do those devices actually provide a reduction drive? From the pictures I've
seen, the just look like a turns-counting knob as would be used on a multiturn
pot. If the standard pot knob, they would provide a 1-100 scale over 360 degrees
of rotation, thus allowing the BFO to be returned to a precise setting, but not a
gear reduction.
Date: Sat, 16 Sep 2006 20:48:11 -0500
From: Tom Norris <r390a@bellsouth.net>
Subject: [R-390] Staggertuned IF's and the 1956 TM

For folks that don't have a copy of the older manual to compare and contrast
procedures, I did up a pdf of the alignment procedure from that year. It includes
a couple real, honest to goodness halftones of the two versions of the if
subchassis. That manual is chock full of photos that look like photos rather than
bad photocopies like in many of the logsa manuals.
IF deck tips                                     page 262

As far as R-390A's go, that's a pretty significant year. If you look in most of your
later change lists, that year's Motorola contract - 0014-PH-56 - incorporated a
majority of the listed changes*. 1956 was also the year after Collins' last R-390A
contract**; Motorola would build only one more run under contract 14385-PC-
58-A1-51. These two Motorola contracts introduced the new specification of
fused B+ lines, with a production mod starting with s/n 2683 of the 1956
contract. None of this counts any of the special Navy mods and I'm sure folks
that had to wrestle the things in the field can think of many more mods and
changes. (not counting those in changes 1 through 4 to the TM) The basic theme
of this email was "1956" so I just stuck to it.
Date: Sun, 17 Sep 2006 08:48:05 +0100
From: "Lester Veenstra M0YCM" <m0ycm@veenstras.com>
Subject: RE: [R-390] BFO Turns Counter (was RE: Spinner knob for

Actually, the "gear reduction" function is already there in the multi-turn BFO
design. It's the larger knob amd the position readout that make the utility. And
yes, when you get what you need from the discard pile, I could use two more.
My the way, I think they are still available new as controls for ten turn pots
Date: Sun, 17 Sep 2006 12:37:02 -0700 (PDT)
From: Masters Andy <nu5o@yahoo.com>
Subject: [R-390] Go figure

Good afternoon group. For the past day and a half I have been chasing down a
problem in my R-390A. I made a mod to the AGC circuit to get AGC action more
to my liking in the CW mode (Mine has the Lanksford AGC mod). I also relaced
a few old caps on the IF deck while in there. Put it back together and started
listening. Everything was lovely for about 2 minutes and then all signals
disappeared. Hauled out the service monitor, counter, scope, voltmeter, etc and
began scratching... A few minutes ago I decided to do something simple. I began
with a visual inspection of everything with the receiver on and as I came to the
oscillator deck, I noticed the 6AK5 was cold and had no filament light. So I pulled
the tube, checked for filament voltage (which was present) and then replaced the
tube. Presto-all works great again. Just because their is no correlation between
work done and radio failures apparently doesn't mean that every once in a while
something will happen concurrently just to teach you to keep your hands out of
it if it is working!
IF deck tips                                     page 263

Date: Sun, 17 Sep 2006 16:05:00 EDT
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] Staggertuned IF Question

>Is it possible to switch filter covers between a straight-tuned deck and a
stagger-tuned deck?

Only with a change in metal. Down at the base there is some metal that sticks out
under the edge of the cover can. You need to cut some clearance if you swap
Date: Sun, 17 Sep 2006 18:38:44 -0400
From: Mark Huss <mhuss1@bellatlantic.net>
Subject: Re: [R-390] Staggertuned IF Question

I suppose you could put a dimple cover on one that had a flat cover. The other
way will probibily short out the trimmers on top of the filters. At least that is
what I think happened. They needed more clearence, but did not want to extend
the center mounting spacer, so the lengthened the height of the can, and dimpled
the mounting hole.

And double check the alignment instructions on the old origional IF deck
without the top trimmers. This was 40 years ago, and we were damn busy. As
for the question of how you aligned for phase on the R-725. You absolutely
used a sweep generator. Don't remember the nomenclature, but compared to
nowdays, it was primitive. Had a big dial for tuning, and a pot to adjust sweep
width. Had markers, though. And you had to use the X-Y of a seperate scope,
along with a detector.

Never looked inside one, but it probibly had a wobulator for sweeping, it was
that old. Anyway, you aligned it to be as flat as possable, and trusted to God and
the Engineering to get the phase right. A final check was to take it out to a TRR-
20 and check the direction and width of the lobe on the scope using a target
transmitter. I suppose they had the equipment to do it right at Vint Hill Farms.

But us poor techs working out of the back of a Duce-and-a-half never saw it.
And I never saw an example of one that was bad unless we deliberately
mistuned the IF Deck. One thing I did notice, for what it is worth. You could
easily get 6dB better S+N/N out of an R725 than you could get out of an R-390A.
I always suspected that this was because that for all intents, the IF bandwidth
after the mechanical filters was wide open. All the noise from the first IF amp
made it to the detector. On the R-725/R-390 IF decks, this is not the case. I think
I remember Lankford adding a post amp filter and finding about the same thing.
Also, the VFO has some extra stuff added to reduce phase noise.
IF deck tips                                     page 264

Date: 28 Sep 2006 15:49:57 -0000
From: "n4buq@knology.net" <n4buq@knology.net>
Subject: [R-390] Staggertuning IF transformers

Still curious about the IF transformers in my current project. As I've mentioned,
I can't seem to staggertune this deck although from all indications, it should be
possible (dimpled filter cover with trimmers on both sides indicating a newer
deck that should be capable of staggertuning). I see where there are resistors
across the primaries of the IF transformers. I assume these are there to lower
the Q of the circuit and thereby increasing its bandwidth. Is it possible the
non-staggertunable decks have transformers without these resistors (or perhaps
some resistance values provide for a broader bandwidth)?
Date: Fri, 29 Sep 2006 19:30:00 +1000
From: "Bernard nicholson " <vk2abn@bigpond.net.au>
Subject: [R-390] IF Tran Resistors

If you snip the resistors in the IF transformers it will increase the gain like you
wouldn't believe, but the signal to noise ratio will be lousy, I spent a couple of
hours the other day repairing a 75A4 for a friend and there was an excess of
gain, eventually I traced it to the resistor in the IF trannie, my friend was a 6
meter fanatic and was using it as a tuneable IF , and at some time he had done
the deed and then forgotten.
Date: Fri, 29 Sep 2006 19:53:11 -0700 (PDT)
From: Perry Sandeen <sandeenpa@yahoo.com>
Subject: [R-390] Blocking capacitor question

It is almost universally accepted that the original C553 0.01mf 300 WVDC 20%
paper should be replaced with a 600 volt "orange drop" type of film cap. My
question is: can one use a .01 1KV volt disc ceramic as well or is there a "gotcha"
that makes using ceramics an un-good idea? Thoughts appreciated.
Date: Fri, 29 Sep 2006 20:35:06 -0700 (PDT)
From: "Jon L. Turner" <ka0ofp@yahoo.com>
Subject: [R-390] AGC Problem

I have a R-390A by EAC. It is my favorite receiver of all the receivers that I own.
A few Saturday mornings ago when I turned it on the signals were distorted and
did a little check. I found that I had no AGC. I put another IF Deck in to see if I
could isolate the problem and the receiver worked fine. What I have found is
that the 180 volts that is to be on pin 5 of V508 is not there. The resistance of 65k
is not there also. I am seeing the 65k the other side of Z503 transformer but not
on the pin 5 of V508. Pin 5 of V508 is connected to one side of the transformer.

It is looking like Z503 has opened. The voltage and resistance readings are out of
the Y2K Manual. Any thoughts would be appreciated.
IF deck tips                                     page 265

Date: Sat, 30 Sep 2006 00:01:25 EDT
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] AGC Problem

These things can some times be fixed. The little wire breaks off in the can. The
cans have large wires that go from top to bottom and make up the bottom
terminal under the deck. In the can, the little coil wire comes out and is wrapped
around this larger wire. Often the little coil wire opens. It hangs in free space
between the coil of wire and the larger wire post. Vibration does the free
hanging wire in. These things also do cold solder joints. Pull the deck out so you
can get it under the magnifying glass. Pull the cover off the offending can. Give
it the real eye ball and set what come loose. If you ohm it and find the coil open
inside, you can still do a can transplant. That's a good after noon once you get a
new to you used transformer. Just takes time to get er done. Not real hard just a
long job.
Date: Fri, 29 Sep 2006 22:48:48 -0700
From: "Bill Feldmann" <n6py@qnet.com>
Subject: Re: [R-390] Blocking capacitor question

I'm using a .01 1000V disc ceramic in mine and it work great. Some fellows feel
the film type caps are better at audio frequencies but at 455kc I don't think it
makes any difference.      Bill N6PY

PS: I just installed the after market 2.5kc and 6kc filters in my R-390A and they
really work fine. But the insertion loss is a lot lower so to keep the carrier meter
readings consistent between filters since I still have the stock 4kc and 8kc filters, I
put a 27K resistor across the input of each of the new filters. I tested the filters
with and without the resistors and no difference in receiver noise floor or 3rd
intermod performance. I now have for filters 2.5kc, 4kc, 6kc and 8kc. This
works out perfect for both AM phone under all conditions and SSB.
Date: Sat, 30 Sep 2006 13:36:26 -0400
From: 2002tii <bmw2002tii@nerdshack.com>
Subject: Re: [R-390] Blocking capacitor question

> My question is: can one use a .01 1,000 volt disc ceramic<snip>

It'll work, but for three reasons the film capacitor is better. First, the leakage of
ceramic caps is higher than film caps, so film caps are better at blocking DC.
Second, and related, ceramics are more likely to fail shorted than modern film-
and-foil caps (though not more likely than aging paper caps), and a short at C553
is particularly unfortunate. And third, ceramic caps distort through-signals much
more than film caps do because of the much greater nonlinearities in the
dielectric. While a ceramic IF blocking cap won't "sound bad" in the same direct
way that a ceramic audio coupling cap can, this distortion acts as a mixer and can
(at least theoretically) raise the spurious response of the receiver. <snip>
IF deck tips                                     page 266

Date: Sat, 30 Sep 2006 16:45:49 EDT
From: Flowertime01@wmconnect.com
Subject: Re: [R-390] BFO Turns Counter info

Would you please do the scan and put the pages on a web site for us. Many of
the fellows would like to have the pages to add to their books. Hopefully we can
get them into the updated web book.
Date: Sat, 30 Sep 2006 16:49:47 -0400
From: Rbethman <rbethman@comcast.net>
Subject: Re: [R-390] BFO Turns Counter info

No problem! I'll get it scanned this weekend, and put both side on my site for
anyone to grab. I'll post the link as soon as I "Git R Done!".
Date: Mon, 02 Oct 2006 10:05:06 -0400
From: Rbethman <rbethman@comcast.net>
Subject: [R-390] BFO Counter info on my site

The following is the link(s) to the doc(s) for the Litton mdl 1309 BFO counter. *
WARNING * THE BMP files ARE about 7MB in size!! This is up for the FEW that
want the info for the NEW MANUAL!!

Date: Mon, 02 Oct 2006 10:43:14 -0400
From: Rbethman <rbethman@comcast.net>
Subject: Re: [R-390] BFO Counter info on my site

The counter info sheet is indeed LARGE for the "manual". IF it is too large, let me
know and I'll reduce its size while TRYING to keep the image clean, clear, and
Date: Mon, 02 Oct 2006 10:51:17 -0400
From: Rbethman <rbethman@comcast.net>
Subject: [R-390] Pics of BFO COUNTER

And for "whatever" it may be worth, the price sticker on the end of the box:
$16.00 . Pictures of the BFO Counter made by litton are ALSO available at:

IF deck tips                                     page 267

Date: Mon, 02 Oct 2006 11:52:48 -0400
From: Rbethman <rbethman@comcast.net>
Subject: [R-390] Counter Base

After looking at the Litton counter closely, in particular the base, I would
conclude that "making" one would be VERY difficult. This is especially true as the
"locking" mechanism is built into it. This is a large "fender" washer insert that
incorporates four spring elements that "lock" the counter and prevent it from
rotating. It is a "pot metal" casting with precisely located holes for mounting the
"head", and the above mentioned assembly. Without a lathe AND a mill, I would
NOT tackle this myself. Another list member acquired a "used" counter from
Date: Tue, 3 Oct 2006 08:57:16 +0200
From: "federico" <federico@dottorbaldi.it>
Subject: Re: [R-390] Pics of BFO COUNTER

Very interesting, I have some surplus that I got from a dismantled radar test
equipment years ago. I never mount the microdials onto my R-390As but I think
that it should be an interesting implementation to the "llook" of the Rx. I read
that they were employed by NSA to have a better understanding of foreing
languages or (in my personal opinion) for easiest RTTY tuning.
Date: Tue, 03 Oct 2006 11:23:48 -0400
From: <mfisch@kent.edu>
Subject: [R-390] BFO multi-turn knob+ Bourns near equivalent

check out: http://www.bourns.com/components.aspx?
cmsphid=7631383|7163299|4657078, and click on the info for the ones that look
similar to the figures we've seen, Might this work?
Date: 3 Oct 2006 18:08:10 -0000
From: "n4buq@knology.net" <n4buq@knology.net>
Subject: Re: [R-390] BFO multi-turn knob+ Bourns near equivalent

Maybe a little circuit that counts the BFO and shows the +/- difference between
the current setting and 455kc, perhaps in 100cps increments and fed to a small
LCD display?
Date: Tue, 3 Oct 2006 13:26:21 -0500
From: mikea <mikea@mikea.ath.cx>
Subject: Re: [R-390] BFO multi-turn knob+ Bourns near equivalent

Sounds good. I think I could do that in between 30 and 100 tubes. To do it all
Glowbug-style, wecould use some of those fancy Burroughs decade-counter
IF deck tips                                     page 268

Date: Tue, 3 Oct 2006 13:51:58 -0500
From: "Cecil Acuff" <chacuff@cableone.net>
Subject: Re: [R-390] BFO multi-turn knob+ Bourns near equivalent

While you are at it lets get rid of the rattling mechanical frequency display and
put a real live digital display in it's space that shows the actual frequency one is
on by counting the frequency results of the PTO and the various conversions.....
that shouldn't take more than another 30 or 40 tubes huh? We'll call it the R-
390B....I guess that would stop the "Non-A" description because we would
actually have to use the radio's nomenclature to communicate which one were
talking about...
Date: Tue, 3 Oct 2006 15:30:58 -0400 (EDT)
From: John Lawson <jpl15@panix.com>
Subject: Re: [R-390] BFO multi-turn knob+ Bourns near equivalent

Y'all keep yore cotton-pickin' hands OFF my Veeder-Root! Wouldn't be a '390' if
it didn't make that lovely, complex machine-y "sound" while idling thru the
bands, looking for an SSB/QRM-less window in the AM window. Although the
previous suggestion of an all-vacuum tube BFO pitch display might be alluring...
and I think it could be done nearer the 30-tube figure, counting the Nixies for
Date: Tue, 03 Oct 2006 16:43:05 -0400
From: shoppa_r390a@trailing-edge.com (Tim Shoppa)
Subject: Re: [R-390] BFO multi-turn knob+ Bourns near equivalent

The HP counter modules used 4 tubes (twin triodes) per decade. They also had a
bunch of neon bulbs and (if a nixie display) used CdS photocells for reading the
neon bulbs and turning them into a nixie readout! Really massively clever! I'm
guessing a BFO readout would usefully display to the nearest 10Hz and max out
at a few kHz, so you'd want two or three decades of counting. That's only 8 or
12 tubes for the counter and maybe a couple more for the gating etc. Of course
the reference for the 10Hz count window would be done with a tuning-fork
reference and a electromechanical divider (think of the old humming Bulova
Acutrons). In fact lots of 60's-milspec-space-age instruments used these sorts of
references. I suspect that even harder to find than 4kc mechanical filters would
be the Bulova Acutron modules!
Date: Tue, 3 Oct 2006 16:01:31 -0500
From: Tom Norris <r390a@bellsouth.net>
Subject: Re: [R-390] make knobs for R-390 series?

Hank Arney here on the list already offers such a thing, he has all three sizes,
CNC machined, powder coated and pretty much at what it cost to have them
done - it's not a project he's making any money on. If the students are going to
do them as a fund raiser, I'm not sure they'd offer them for much less. He has
machined gear clamps, oldham coupler disks, and R-390 "green gears" as well.
IF deck tips                                     page 269

(unless he's out of some of them) One thing I don't think he has are oldham
coupler disks for R-390 crystal decks and the odd coupler the R-392 uses for it's
bandswitch shaft. Those might some good short-run projects. Maybe.
Date: Tue, 3 Oct 2006 16:38:57 -0500
From: "Bill Hawkins" <bill@iaxs.net>
Subject: RE: [R-390] BFO multi-turn knob+ Bourns near equivalent

I still have some IBM 704 plug-in tube units, about 8" high by 10 wide by 1.5
deep, with eight 9 pin sockets and many terminal points. No sockets for the PIU,
though. Some even have IBM brand tubes, almost all twin triodes. Don't have
room for them in the 390, but it would be equipment from the same period.
Date: Tue, 03 Oct 2006 17:52:55 -0400
From: Mark Huss <mhuss1@bellatlantic.net>
Subject: Re: [R-390] BFO multi-turn knob+ Bourns near equivalent

Anybody know how fast a Dekatron would count? These were tubes with a
circle of neon dots on the front. You fed it pulses, and it would move the lighted
dot around the circle. A divide by ten counter and display in one!

Date: Tue, 3 Oct 2006 18:04:35 -0400 (EDT)
From: John Lawson <jpl15@panix.com>
Subject: [R-390] Dekatron counting speed

I'll need to get home and pull the datasheet - IIRC the usual Sylvania or RCA
Dekatron had a transfer-rate of about 400 - 500 KC, ie. you could drive them at
500KC and get a divided-by-ten pulse of 50 KC. I have upwards of 40 of 'em,
(none for sale/trade currently) and sockets and biasing networks too. Someday
I'll make a Grand Project out of them - or a few, at any rate.
Date: Tue, 3 Oct 2006 18:57:13 -0500
From: Tom Norris <r390a@bellsouth.net>
Subject: Re: [R-390] BFO multi-turn knob+ Bourns near equivalent

Well, the nomenclature would depend on which of the two radios that would be
converted, so the R-390 would end up being the R-390B and the R-390A would
end up as and R-390C, then there are things such as fully synthesizing it -
internally, not like the GRC-129, so I suppose that would add another letter.
Then there is the Keilbasa ballast mod...
IF deck tips                                     page 270

Date: Tue, 03 Oct 2006 22:42:15 -0400
From: Mark Huss <mhuss1@bellatlantic.net>
Subject: Re: [R-390] BFO multi-turn knob+ Bourns near equivalent

For the counter, you would have to use NIXIE tubes, of course. 2.6 by 0.5 inches,
6 digits (100 Hz). About the smallest NIXIE you can buy is an IN-17. It is 0.56"
wide, so you need at least 3.4" for display width. You are going to have to
rework the front panel for this. But it would be beautiful!
Date: Tue, 03 Oct 2006 22:50:54 -0400
From: Mark Huss <mhuss1@bellatlantic.net>
Subject: Re: [R-390] BFO multi-turn knob+ Bourns near equivalent

You know, if you actually sat down and designed it from scratch, you could
probibily get away with a lot less tubes than you think. Using mixers to derive a
single frequency that is the sum of the three oscillators, Simple ring counters
using decimal rather than binary logic, etc. Trying to get it into the case,
Date: Wed, 4 Oct 2006 15:22:42 -0500
From: Tom Norris <r390a@bellsouth.net>
Subject: [R-390] New Counter Dials Available

Bourns still makes counter dials, and they aren't that expensive. Allied and
Newark appear to carry most of their line and others. Here's the Bourns counter
dial catalog -- http://tinyurl.com/fnodk

The "odometer" style, their p/n CT23 is a smidge over $22.00 from Allied,
probably a similar price in the Newark catalog. This style knob is close to the
older Veeder-Root, though I'm not sure if it has a "-" after 00.0, it's probably 00.0
- 24.9. Both Allied and Newark have the analog sort of dial, as well as some very
expensive dial and counters that are mostly identical to the Bourns. There is also
an inexpensive single turn calibrated dial carried by Allied, Digi-key, Farnsworth
and others made by Kilo International. (on this page)


Plain old analog dial, but only 1 turn instead of 10. Around $13 Just some
options since I've not heard back from Fair Radio this most recent email query.
Date: 16 Oct 2006 14:29:03 -0000
From: "n4buq@knology.net" <n4buq@knology.net>
Subject: [R-390] Latest R390A Project (long)

I replaced the capacitors and resistors in the IF transformers with little (if any)
improvement to the IF alignment this last weekend. I mentioned earlier that it
appeard one of the slugs was at or near it end of travel before I got to the peak
point. Thinking it could be an out-of-tolerance capacitor(s), I replaced them.
IF deck tips                                    page 271

After replacing these components, the slug peaked in about the same position as
before. Determined, I cranked down on it just a bit harder and noticed the coil
form was turning just a bit. Fortunately, there is sufficient slack in the Litz wires
so they weren't damaged. I epoxied both of the coil forms in T501 and T502 so
they shouldn't be going anywhere soon. I can crank the slug sufficiently now to
get to both "sides" of the peak so it looks like I'm "done" in that area. Still can't
stagger-tune the thing, though.

I did notice I got a much strong Diode Load reading when in the 2kc position as
opposed to the other filter settings. Turned out that the lower trimmer caps
were way out of position. After setting them, the various filters now have close
to the same Diode Load reading. There's a little variation, but I assume that's
expected as each filter ages differently.

I then started looking at the AGC action. I've mentioned before that SLOW AGC
produces an increase in gain than the other AGC settings. I hooked the scope to
the IF output and monitored it in all three settings. The MED and FAST settings
seem to keep the IF output level fairly close to the same values when receiving a
strong station. Switching to SLOW causes the IF voltages to increase
substantially (maybe a factor of 3 or 4 times that of MED or FAST). It seems to
distort just a little on SLOW mode as well, particularly on strong BC stations.

I then watched the AGC voltages last night. All three postitions yield very close
to the same value (about -2.5V if I recall correctly). Switching to AGC causes the
voltage to climb nicely to that point. If I switch from FAST to MED, the voltage
stays nearly the same level. Switching from MED to SLOW causes the AGC
voltage to drop considerably (nearly zero) and slowly climb back to -2.5V
(assumably as the 2uF cap charges). Switching from SLOW to MED or FAST
causes the AGC voltage to spike as the cap discharges and then the voltage
settles back to -2.5V. I would think the AGC voltage action above seems normal,
yet I'm getting the distortion on SLOW AGC with the IF output being too high in
that postition. Any ideas what might be wrong? I assume this isn't the correct
behavior.Thanks! Barry - N4BUQ
Date: Tue, 17 Oct 2006 16:39:45 -0400
From: "Drew Papanek" <drewmaster813@hotmail.com>
Subject: [R-390] Re:Latest R390A Project

>Switching to SLOW causes the IF voltages to increase substantially (maybe a
>factor of 3 or 4 times that of MED or FAST). It seems to distort just a
>little on SLOW mode as well, particularly on strong BC stations.

The classical cause of that problem is leakage in the 2uF chassis-mounted AGC
integrator capacitor. I experienced that problem; replacement with an under-
chassis mounted new film type cap cured it (left old disconnected cap in place on
chassis for appearance sake).

[see rebuild tips in Capacitors].
IF deck tips                                     page 272

>I then watched the AGC voltages last night. All three postitions yield
>very close to the same value (about -2.5V if I recall correctly).

How close is "very close"? Because of the large number of gain-controlled stages
in the R-390A, a small change in AGC voltage has a relatively large effect on
gain. It doesn't take much leakage to drag the AGC voltage down just a smidge
thereby causing the problem you report.
Date: 17 Oct 2006 21:00:13 -0000
From: "n4buq@knology.net" <n4buq@knology.net>
Subject: Re: [R-390] Re:Latest R390A Project

Probably less than 0.2V. I figured a badly leaking cap would have made a
greater change than that but maybe not. I plan to replace it. Thanks,
Date: Mon, 27 Nov 2006 13:58:34 PST
From: Gary Gitzen <r390a@uwave.com>
Subject: [R-390] R-390 <> R-390A IF decks?

I _may_ have the opportunity to obtain an R-390 IF deck. I'm wondering if it is a
"drop in" to an R-390A? What (any?) changes are needed, other than possibly
tubes and fil wiring? Is this a "good thing to do"? While I love the steep skirts of
the 390A IF deck's filters, I've heard Very Good Things about the R-390 IF deck's
L-C sound. Thanks for any help/info/insights.
Date: Mon, 27 Nov 2006 14:46:50 -0800 (PST)
From: "Tom M." <courir26@yahoo.com>
Subject: Re: [R-390] R-390 <> R-390A IF decks?

I wrote a procedure to do what you're asking. To answer your questions simply,
it's not a drop in, but it's not rocket surgery either. See this link:

Date: Tue, 28 Nov 2006 09:31:35 -0800
From: "Dan Merz"
Subject: RE: [R-390] R-390 <> R-390A IF decks?

Gary, I used Tom's instructions for putting the 390 IF deck in my 390a. It
worked well and is still in my receiver. I wouldn't classify it as a casual job
because of the tight quarters for moving connections around on the bottom side
of the chassis, mostly to get the filament circuitry rewired. The instructions were
very clear about what to do and I was happy with the result. Good look on
getting the R-390 deck - it took me a year or more to find one. <snip>
IF deck tips                                     page 273

Date: Fri, 15 Dec 2006 14:43:17 -0600
From: "Dave Faria" <Dave_Faria@hotmail.com>
Subject: [R-390] Spectrum Analyzer For trade

GM List. I have for trade a Panoramic Spectrum Analyzer Model SB-15A by
Singer. It was a project I started abt 5 years ago. All I have done is clean the
unit. I have the depot aintenance manual(copy from Fair Radio). The analyzer
will power up and take a signal from a signal generator but, there is a problem
with the gain. The tuning for the center frequency is off and probably the sweep
width as well. Calibration may just be the problem but, I doubt it, there are
probably other problems. The center frequency is tunable from 0 - 500khz from
manual(name plate says 100 to 600khz) and sweep dial 1 to 200khz. Anyway,
what I'm looking for is a R-390A I can use to build a R-725. The radio does not
have to work but, the modules need to be complete with no corrosion. Grease is
OK - I can clean the radio and rebuild the gear train. It would be nice if the panel
is engraved or in good shape if silk screened. I can provide pictures of my
Analyzer. Thanks for your interest.                                   Dave Faria           Austin, Tx
Date: Sat, 16 Dec 2006 05:55:26 -0500
From: "Bob Young" <youngbob53@msn.com>
Subject: [R-390] unstable BFO note on R-390A

I use the BFO frequently to zero beat the carriers on BCB. It is off by maybe 200
CPS for one thing after moving the BFO knob as much as it could go to one side,
is this an easy fix to align the BFO? Also although I feel no backlash it is jumpy
when tuning with it on. If I move the tuning knob up and down the BFO will
jump to differing frequencies and sometimes stay off center. One of the springs
on the split gear is shorter than the other, could this cause this problem, or is this
more indicative of worn gears maybe? Any other ideas? thanks, it is worse
when warm.
Date: Sat, 16 Dec 2006 05:48:30 -0800
From: "Dan Merz" <mdmerz@verizon.net>
Subject: RE: [R-390] unstable BFO note on R-390A

Bob, yes it's an easy fix to "align" the bfo. Loosen the set screw on the knob,
remove the knob, set the bfo at the correct frequency of the center of the i.f. by
"zero beating" the noise (or on a signal that you know is coming down the center
of your i.f., for example thru the xtal position) and then without moving the
setting, reinstall the knob with the indicator at the top zero position. I'm not
sure what gear you are talking about as the bfo shafts on my radios go straight
into the coupling to the bfo bellows and turn the pto directly. Perhaps you were
referring to some interaction of zero beat when you were using the main tuning
knob, which has gears. Or maybe you radio is different than mine and has a
geared bfo. There may be a problem with either the coupler on the shaft directly
behind the panel or with the bellows coupler within the i.f. chassis. Can you
peek into the radio from the top and see if the coupler behind the panel is secure.
I've had one of mine fail by cracking and it couldn't be tightened enough to
IF deck tips                                     page 274

be secure. Or perhaps the bfo tube is bad. If you are using the bfo to zero beat
broadcast stations at known frequencies, there is no guarantee that the tuning
indicator will indicate the correct frequency unless you calibrate the main tuning
to indicate correctly on the band of interest and near the frequency of interest,
which is a process separate from the bfo alignment. I would guess the usual
390a will not indicate frequency to within 200 cps (1 division on the wheel)
without calibration on each band even if you align the bfo perfectly, at least mine
won't. I'm happy to be within 1000 cps in going from one tuning range to
another without re-calibrating the tuning indicator on a nearby signal of known
frequency or using the internal calibration oscillator. I recall that my set is only
within about 500 cps in going from one end of the range to the other if I calibrate
it at the middle of the band. And that was after opening and adjusting the range
of the main tuning pto. Old is good but not necessarily as good as it was. Dan.
Date: Sat, 16 Dec 2006 17:18:11 -0500
From: "Bob Young" <youngbob53@msn.com>
Subject: RE: [R-390] unstable BFO note on R-390A

Thanks, but the problem is that there is a flat part on the shaft where the set
screw goes which only allows a little leeway either way for the knob. The gear
I'm talking about is the split gear that is right behind the main tuning knob if I
remember right. It is supposed to eliminate backlash I'm pretty sure. When I
wiggle the main tuning knob with the BFO centered and on I can knock it off
zero beat by wiggling the knob, sometimes it goes back other times no. This is
without turning the knob at all, it will jump all over the place. I'm wondering if
this could be in the VFO or is something in the gearing mechanism or maybe
because the springs are not equal the split gear is not functioning properly? not
sure, oh also when tuning in a station with the .1 khz position it is also very hard
to keep it peaked and tuned it jumps all over the place also along with the BFO if
that helps.
Date: Sat, 16 Dec 2006 17:46:24 -0500 (EST)
From: John Lawson <jpl15@panix.com>
Subject: RE: [R-390] unstable BFO note on R-390A

Bob - it might be a Good Thing to check the output of the PTO for any unstable
FM - if the radio cannot hold a stable setting in the 0.1 Khtz BW position, with the
BFO off - the problem is maybe in the main frequency determining circuits, I
would think... However if the tuning is stable with the BW set to 0.1, and the BFO
off - of course this can be checked against WWV - but starts jumping around
when the BFO is turned on, then it's as you surmise - the BFO itself has gone
wonky on ya. Could there be gunk in the BFO variable capacitor?
IF deck tips                                     page 275

Date: Sat, 16 Dec 2006 14:48:10 -0800 (PST)
From: Joe Foley <redmenaced@yahoo.com>
Subject: Re: [R-390] unstable BFO note on R-390A

No, maybe not. Have you adjusted the frequency readout with the ZERO
ADJUST knob yet? It disconnects the gears from the KC CHANGE knob, that
may be where your 200 CPS error is coming from.

>is this an easy fix to align the BFO? Also although I feel no..........................

Is there a spring on the Oldham coupler on the PTO shaft? While you're looking
in there clean the flat pointed spring that rides on the PTO shaft, but don't oil it,
leave it so it can make an electrical contact to the shaft.

>One of the springs on the split gear is shorter than the other, <snip>

Make sure you do this after at least a one-hour warm up so everything is as
stable as it can be. Some frequency change while warming up is,....... acceptable,
... I guess. Ok, its tubular, it happens with tubes!
Date: Sat, 16 Dec 2006 15:21:55 -0800 (PST)
From: Joe Foley <redmenaced@yahoo.com>
Subject: RE: [R-390] unstable BFO note on R-390A

> Thanks, but the problem is that there is a flat part <snip>

You need to look behind the front panel for a coupling in that shaft, it has one of
those clamps you find on the gear shafts, you'll need a Bristol wrench for the set

> The gear I'm talking about is the split gear that is <snip>

Check the setscrews on the Oldham coupler sections, they may be loose.

>When I wiggle the main tuning knob with <snip>

Also, look at the back of the BFO knob, it has a detent lug that keeps it from
being turned more than one full turn, that has to engage the stop at the bottom
of the shaft hole, that knob has to be slid on far enough to engage that but not so
far as to rub the panel.
IF deck tips                                     page 276

Date: Sat, 16 Dec 2006 16:25:08 -0800
From: "Dan Merz" <mdmerz@verizon.net>
Subject: RE: [R-390] unstable BFO note on R-390A

"Thanks, but the problem is that there is a flat part on the shaft where the set
screw goes which only allows a little leeway either way for the knob."

I forgot about the flat on the shaft which means you have to make thadjustment
I mentioned using the coupling between the shaft sticking out the front panel
and the shaft going into the i.f. chassis, by disconnecting this coupling behind the
panel, adjusting the bfo frequency with the shaft going into the i.f. chassis and
then reconnecting with the knob pointing at zero. But it sounds like you have a
problem with the main tuning so this adjustment should probably only be done
after you clear up the main tuning problem if that's the cause of what you're
experiencing. You need an independent way of monitoring the bfo frequency to
see if it's actually changing or whether the change in beat note frequency is due
to change in the main pto jumping around in frequency. I seem to recall that I
used a signal generator to see what my center i.f. frequency was and then I set
the output of the bfo to that using a frequency meter and then connected the
front shaft with the bfo producing that frequency. Without the
signalgenerator/freq meter, zero beating the noise is about as good a method
to get the bfo at the right frequency before tightening the clamp between the
two shafts behind the panel. Dan.
Date: Sat, 16 Dec 2006 18:25:54 -0800 (PST)
From: Joe Foley <redmenaced@yahoo.com>
Subject: RE: [R-390] unstable BFO note on R-390A

> what exactly is the Oldham coupler anyway?

If you turn the radio upside down and remove the bottom cover you will see the
PTO. If you follow the operating shaft toward the front panel you will see a
coupling that allows some deflection of that shaft, that is the Oldham coupling.

It has three parts, four if you count the spring, which is sometimes missing. The
spring is to keep backlash out of the coupling sections, it SHOULD be hooked to
the two pins that stick out of the outer sections of the coupler.

There should also be some gap between the three sections, about 1/32" should
be enough. NOTICE: If that gap is not there it could cause just the problem you
have, jumpy tuning, because it is putting pressure against the insides of the PTO.
I just remembered that from one of Nolan's posts from the past. Also, check the
mounting of the PTO,.... just because.
IF deck tips                                     page 277

Date: Wed, 20 Dec 2006 21:18:53 -0500
From: "Bob Young" <youngbob53@msn.com>
Subject: [R-390] warbling BFO problem solved

>2. Now for the warbling of the beat note. There is a small strap that is
mounted.............. the BFO centering procedure is on Chuck Rippels web site
www.r390a.com..............there is also a lot of information at
      http://www.r-390a.net/Pearls/ concerning VFO/BFO

I tried this and it worked like a charm, the BFO note is now clear, louder and best
of all smooth into and out of zero beat, no more jumping around. It did sound
like a bad connection which is why I tried this first. I'm now waiting for a whole
set of Bristol wrenches so I can loosen the little clamp behind the face of the radio
to center the BFO and I'll be all set, thank you all for your help.
Date: Wed, 20 Dec 2006 18:27:42 -0800 (PST)
From: Joe Foley <redmenaced@yahoo.com>
Subject: Re: [R-390] warbling BFO problem solved

One more thing to do while you're in that area, Bob.

Loosen the bushing on the KC CHANGE shaft where that shaft goes through
the front panel, there are three bushings on that shaft, it isn't easy to get all three
to line up perfectly, two wouldn't be so hard.

Also, that shaft may have some bend in it, so what we usually do is to leave the
one on the front panel "just snug".
Date: Fri, 2 Feb 2007 12:04:59 +1100
From: "pete williams" <jupete@bigpond.net.au>
Subject: [R-390] Transplanting R-390 IF modules to R-390A

Convention has it that directly substituting the R-390 IF module to a R-390A to
simulate a R-725/URR wasn't possible without making changes to the heater
wiring. Reason being the original R-390 module was wired for a 25V heater
and the R-390A used 6.3 V. It was further assumed that the transformer of the
R-390A had insufficient capacity if its 26V secondary was used.--- the 6.3 V line
was ample. Not impressed with the work needed to rewire in a cramped
environment, a look at the heater layout for both receivers in the IF area,
showed the following. The R-390 needed 25V on pin #20 from the plug P-117 .
On the R-390A, pin #20 had 6.3 V.also, the R.390 needed 6.3V on pin#8 from
the plug P117.. On the R-390A, pin #8 had 25V.

Question..1.. why not transpose wires on pin #20 and #8 and satisfy the
voltage requirements without the hard work?

Question 2.. would the xfmr in the R-390A handle the extra demand?
IF deck tips                                     page 278

Doing it and measuring the results gave the following.......Total current from
the 25V tag on the xfmr was 1.2 A with 12BW4 tubes as rectifiers, and 3TF7 in
use.--- just on the maximum continuous rating for the xfmr. Obviously would be
less if SS diodes used in lieu of tubes. Current drain on switching to CAL rose
to 1.45 A but well within the 4.6 A allowed on a 70% duty cycle (see xfmr specs)
RESULT.. No problems experienced with Xfmr heating or drop in voltage...
and the radio performs. Changing the pin connections as outlined in P -117 not
too difficult. These results do NOT include the use of the switched ovens but it's
your choice.

NOTE.. further reduction of the 25V current drain could be achieved by
removing the ballast tube , running a connecting wire from pin#8 to pin #19
and chassis grounding pin 7 of the ballast tube socket. This the allows 6.3 V
to be applied to the BFO and VFO tubes .You'll need to be running 6BA6. The
army specs would, no doubt be exceeded but then as casual users we don't
run 24 7 365!-- do we.? Maybe it's a reinvention of the wheel, but if so I
haven't had it rotated here. Thanks to Gary Gitzen and Tom Marcotte who
have both been across these developments. Any questions?

Pete D..Williams
Date: Fri, 2 Feb 2007 09:42:54 -0600
From: mikea <mikea@mikea.ath.cx>
Subject: [R-390] Re: [Milsurplus] Transplanting R-390 IF modules to R-390A

>....... but why would you want to substitute a IF deck with mechanical filters to
one without?

The mechanical filters tend to "ring" a bit, in my experience, where the LC filters
don't. If you need better phase-flatness across the filter passband, the LC filters
are preferable to the mechanical ones, and it's my understanding that that's why
the R-725 RDF receiver used the R-390 IF deck in the R-390A chassis. I could be
all wet, of course; it wouldn't be the first time.
Date: Fri, 02 Feb 2007 12:18:11 -0500
From: Mark Huss <mhuss1@bellatlantic.net>
Subject: Re: [R-390] Re: [Milsurplus] Transplanting R-390 IF modules to R-390A

Indeed, as an experiment I once dropped an R-390A into a TRR-20 (a DF set that
used a commutated ring of vertical antennas for DF). Result was a much wider
propeller, I.E. the resolution was not anywhere near as good. I was later told that
was because (1) phase-shift in the mechanical filters, and (2) phase noise from the
PTO. The R-725 addressed both these issues. And Ray, One thing we noted,
having aligned both R-390A's and R-725's, was that as a rule the R-725's almost
invariably had a better S/S+N sensitivity rating. We always suspected this was
because the R-390A's noise floor is determined by the IF deck, not the First RF
amp, as is usual. And the R-725, with it's R-390-style IF Deck had bandwidth
IF deck tips                                     page 279

filtering throughout the chain, not just a lump at the input. That they also
decoupled just about every line out of the PTO and into the IF Deck with ferrite
beads probably did not hurt either.

Finally, we used the Shop R-390A as a Shop Radio, with a used stereo speaker.
On someones suggestion, we tried an R-725. And it sounded a lot better, to us, at
least. Enough better that we put an R-390 IF deck on order and modified it to
drop into the Shop R-390A. Could have been our imagination. But Ace, a SSG
Hog, often said he could copy in-the-noise code better on an R-725 or old R-390
than on a R-390A. Said it sounded cleaner.
Date: Fri, 2 Feb 2007 11:50:06 -0600
From: mikea <mikea@mikea.ath.cx>
Subject: Re: [R-390] Re: [Milsurplus] Transplanting R-390 IF modules to R-390A

Phase noise problems with the PTO? As in just junk on the PTO output line,
fixable by ferriting it, or other problems that required changes to the PTO other
than just ferrites? Would decoupling the PTO stuff make any audible changes, or
is this just changes in the DF propeller sizes from field measurements? Because if
the R-390 PTO has phase issues, the R-390A PTO probably does, too, and I can
see a purchase from Amidon or an Amidon supplier in my near future.

> Finally, we used the Shop R-390A as a Shop Radio, <snip>..................

I've noticed that as the bandwidth gets narrower, the signals seem to be smeared
out a little bit in time, on the R-390 *and* R-390A, but that effect seems to be a
little exaggerated on the R-390A when I've got the mechanical filters switched in.
I think it's not all due to ringing in the filters, but that there's some analog to
Heisenberg's Theorem that defines a frequency-time product uncertainty that
you have to live with -- something like the product of certainty-in-frequency and
certainty-in-time > some constant K where K is big enough to get bothersome
for really narrow bands.

>But, again, I could be all wet....................

Certainly I do better copying code down in the grass on an R-390 than on any of
my R-390A, and it beats my riceboxes (Yaesu FT-857, FT-857D and FT-897D) all
hollow, even with DSP wound down to 60 Hz. It also helps keep the bedroom
warm at night, which is a big bonus in winter, but not so much in summer.
IF deck tips                                     page 280

Date: Fri, 02 Feb 2007 12:59:30 -0500
From: "Tim Shoppa" <tshoppa@wmata.com>
Subject: Re: [R-390] Re: [Milsurplus] Transplanting R-390 IF modules to R-390A

Noise on an output that is fixable by "ferriting it" is not usually called "phase
noise". Usually phase noise in a MW radio context refers to "close-in phase noise".
Ferrites are usually used to reduce EMI susceptability and/or EMI emissions at a
frequencies far away from the desired frequency. Several of a 390A's oscillators
exhibit FM under B+ and AGC variations. But again that's usually called FM and
not "phase noise". I hesitate to send this e-mail to the list at all because I just make
matters worse by mentioning actual problems in an attempt to get someone to
define their mythical problem.
Date: Fri, 2 Feb 2007 14:17:55 -0500
From: <kirklandb@sympatico.ca>
Subject: Re: [Milsurplus] Transplanting R-390 IF modules to R-390A

Use a filter with a Gaussian response (to 6 or 12 dB points) for minimum ringing,
i.e. for CW. If you design a narrow flat passband, linear phase filter, it will ring
for quite a while. (due to the sharp cutoff corners). I suspect that the tuned
circuit IF lent themselves better to a Gaussian shape unless they were staggered
tuned to get a flat passband.

For CW, a filter with non-linear phase is not that much of an issue. However go
to digital or RTTY, the phase response of the filter becomes more important.
Date: Fri, 02 Feb 2007 11:23:06 PST
From: Gary Gitzen <r390a@uwave.com>
Subject: [R-390] R-390 > R-725 IF filament conversion

Pete forced my hand on this one. I was asleep at the switch.

The following words are musings and ramblings about replacing the IF deck in
an R-390A with the deck from an R-390; in effect recreating the R-725/URR. It
mostly focuses on the widely held belief that major IF deck filament rewiring is
needed for this change. If this doesn't interest you, please punt now. I recently
acquired an R-390 IF deck (thanks, Pete), with the intent of converting and
installing it in one of my two R-390A mainframes. This would give me one Rx
with the mechanical filters, and another with L-C filters. Upon inspection of the
"new" IF deck, I quickly saw why I'd been warned that "it gets real tight in there"
when rewiring the filament string for 6.3V operation. Not a project to be
undertaken without some careful thought and planning. "Why," I asked myself,
"does it need to be rewired?" And I answered myself with "Everybody knows,
dummy, that the R-390A power transformer doesn't have enough 25.2V current
to power the non-A deck in 25.2V mode. You read Tom Marcotte's excellent
writeup on "rolling your own R-725" with a non-A IF deck on his web page, and
others have written about this issue. Shut up, get out your soldering iron, and
start working!" But since "everybody knows" has always triggered my curiosity,
IF deck tips                          page 281

I thought I'd take a better look. I came up with the following 25.2V fil
requirements for the non-A IF deck:
       0.15A 4X 6BJ6
       0.15A 2X 12AU7
       0.15A 2X 6BJ6 + 1X 12AU7
       0.3A 3TF7 + PTO & BFO 6BA6's = 0.75A @ 25.2V
Additionally, 0.15A@6.3V 1X 6BJ6, needed from somewhere.

Yeah, I thought, that 0.75A might overload the 25.2V winding on the xfmr. But
wait a minute: the 390A also has a 3TF7 and its 0.3A load in its IF deck, so we can
eliminate that as an "extra power needed" item. That leaves us with .075A - 0.3A
= 0.45A of "extra" 25.2V current needed for the non-A IF deck. Then I started
looking closer at actual numbers, and how I configure my

First, I never use 3TF7s. I replace the PTO & BFO 6BA6's with 12BA6's, which
reduces the 25.2V filament drain by another 0.15A. It's now down to 0.3A "extra"
needed. Second, I don't use 26Z5s. I replace them with solid-state diodes. 26Z5's
have a filament current of 0.3A each, or 0.6A for two. Hmmmmm......... That's
twice the "extra" filament power I now need for that non-A IF deck. I appear to
have 0.3A of "extra" 25.2V available. I may not need to follow the rewiring
instructions after all.......

I took a look at the power transformer. The 25.2V winding is rated 1.2A
continuous, plus 4.6A at a 70% duty cycle for the ovens. But I never use mine in
an Alaskan igloo with the ovens on. I turn the ovens off, as do most owners of
R-390As. This makes that 70% of 4.6A available; about 3.22A. With that other
"extra" .3A, I have over 3.5A of "excess" 25.2V available.

Conclusions: Simply replacing the 26Z5s with silicon diodes frees up enough
25.2V current to power a non-A IF deck in an R-390A. Even without that change,
the total 25.2V load appears to be easily handled, within spec of the transformer,
unless it is operating at minimum rated temperature with the ovens on. Turning
off the ovens frees up more than enough 25.2V current, even with 26Z5's and

So where did this "everyone knows" come from? Tom Marcotte appears not to
know. He simply duplicated the original R-725 mod as closely as he could. My
_suspicion_ is that everyone just assumed it had to be done that way.

The major benefits of not rewiring filaments for 6.3V appear to be:
1: The risk of damaging the non-A IF deck is reduced.
2: If ever needed, it will be much easier to restore the non-A IF deck so it can run
in a non-A radio. All in all, both of the above could have been a major PITA.

Question for the list: have I missed anything here? Made any incorrect
assumptions? If so, please let me know before I do this. Or stick my foot deeper
in my mouth.
IF deck tips                                     page 282

"That was Yesterday"; now fast forward:

I exchanged mail with Pete Williams, David Wise, and Tom Marcotte a while
back, sending them an earlier version of the above.

Since then, Pete has actually tried it, using an adaptor/extension cable which flips
pins 20 & 8 on the main connector. He reports good/excellent results. I've taken
a cursory look at the connector on the non-A IF deck, and it looks possible to
make the flip there. I'll be trying that "in the near future". More info as I think I
know it, although Pete may beat me to it. Pete also forwarded to me a scan of
the filament wiring schematic from hist R-390 manual. Thanks, Pete!

Tom M suggests adding a B+ dropping resistor inside the non-A IF deck to
reduce B+ to R-390 voltage. Measurements and more research needed.

Thanks to Tom Marcotte for both the excellent R-725 documentation on his web
site and for his encouraging words re the above in private communication. My
compliments and thanks to Pete for once again taking theoretical musings, doing
further research to identify the pin 8 & 20 flip, then actually doing it on his bench.
More kudos for caring enough to take the time to report his findings.
Date: Fri, 2 Feb 2007 11:30:48 -0800
From: "David Wise" <David_Wise@Phoenix.com>
Subject: RE: [R-390] R-390 > R-725 IF filament conversion

When the R-725 was created, the ovens were still a requirement. I speculate that
it didn't occur to Tom that leaving them off opened up the options. This is not a
criticism - it never occurred to me either. I'm glad someone was more awake.
Date: Fri, 02 Feb 2007 15:15:37 -0500
From: Mark Huss <mhuss1@bellatlantic.net>
Subject: Re: [Milsurplus] Transplanting R-390 IF modules to R-390A

Yes, the beads would not do anything about PTO phase Noise, it was just to keep
garbage from getting into or out of the PTO. If memory serves, there was also a
wiring change to the tube, and a few cap changes to try to reduce the phase
noise. The thing I remember the first time I looked under the hood of an R725
was what seemed like hundreds of those beads everywhere. There were also
contact fingers on the bottoms of the RF and Xtal osc chassis. I do know that the
mechanical filters do have a very adverse effect on what is called Doppler effect
DF'ing systems, such as the TRR-20. And though comparatively, the R-390 and
R-390A PTO's do not have that much phase noise, it was really getting
bothersome by the early eighties for the techniques being developed then. I also
know that they went through a whole s**tpot of receivers, including Collins,
trying to find one that had synthesis but less phase noise than the R-390A. Racal
finally came through, but just barely, which is why they won the contract to
replace the R-390A. As to the rest of it, like I said, it could have been our
imagination. It is a fact that getting an R-390A under 1uVS+N/N at 8kc BW
would take a while, and getting the R725 to the same S+N/N was normal after
IF deck tips                                    page 283

the first alignment run-through. Mind you, we swept the R-725 while the R-390A
just got three-point alignment, but what difference that would make, I don't
know. Like I said, the general consensus was that the R-390A IF Deck had a
higher noise floor because from the second IF tube on, the thing was as wide as a
barn door. And yes, we did align them for the full 16 kc bandwidth.
Date: Sun, 4 Feb 2007 04:11:00 -0800 (PST)
From: "Tom M." <courir26@yahoo.com>
Subject: [R-390] R-725 Procedure

Gene, here is the text.Conversion of the R-390 IF Deck for Use in R-390A For
Improved Audio,
Make Your Own R-725

Thomas F. Marcotte, P.E., N5OFF courir26@yahoo.com

 As many of the readers of Electric Radio know, the US Army created a modified
R-390A version for direction finding known as the R-725/URR. I wrote about
this modified radio in this publication a few years ago. The main difference
between a R-725 and the R-390A is that the R-725 utilizes a custom built IF deck
that is very similar in construction to the R-390 IF deck. It has tuned circuit
selectivity instead of mechanical filters. The mechanical filters of the R-390A
created distortion when that radio was employed for radio direction finding use.
In an internal Collins engineering report published in 1952, Lou Couillard wrote
of the improved R-390A, which at that time was called the R-390(XC-3),
"Although the superior shape factor of the mechanical filter IF is desirable in
most applications, consideration should also be given to an alternate tuned circuit
design for use in special applications. The excellent shape factor of the
mechanical filters precludes the possibility of linear phase shift across the
passband. Where a linear phase characteristic is desired such as in direction
finding equipment, a tuned circuit IF is necessary."

Employment of the tuned circuit IF is exactly what was done in the R-725. In
addition to the new IF deck, the R-725 was given a new filament transformer and
a minor modification for the PTO to provide improved stability. Motorola was
awarded a contract in 1956 (476-PH-56-91) to prototype the R-725. I know of a
couple of these Motorola sets existing today.

Packaging of modified sets for quantity DF use were handled by ArvinIndustries
and Servo Corporation of America. Approximately three hundred R-390A's
were modified to the R-725 configuration. These sets are relatively tough to find
today. New IF decks were manufactured by the modification companies
(actually salvaging some of the components from the now junker R-390A IF
decks) and installed in existing R-390A's. The new IF decks were named "SERIES
500 IF STRIP ASSY." They looked almost just like R-390 IF decks (see the
comparison photos), except that the IF connectors were relocated to match the
cables and connectors in the R-390A chassis. The circuits were designed to plug
IF deck tips                            page 284

and play in the R-390A instead of the R-390. The decks are not interchangeable
(until now that is, after performing the modification described herein).

Notwithstanding DF capabilities, a side benefit of the SERIES 500 deck is thatit
provides a smoother sound than does the stock R-390A IF deck. Mechanicalfilters
are said to "ring" and after a while can be fatiguing to the listener. The purpose of
this article shall be to describe how one may "roll his own" SERIES 500 IF deck
from a surplus R-390 IF deck. Please note that I don't advocate trashing of a
good R-390 to do this mod. The IF deck I started with came from a Motorola
junker. I would urge you to likewise find a junker R-390 as a source of an IF
deck for this project . Make sure that the deck is in working condition prior to
beginning the modification.

The R-390 IF deck was designed to operate with one 25V filament supply
(unfortunately the 25V supply available in the R-390A is insufficient to power all
of the filaments in the R-390 IF deck). The R-390A deck was designed to operate
with a combination of 6.3V and 25V filament supplies. The task involved in this
conversion is to rewire the R-390 filaments to comply with the voltages available
in the R-390A and provided at the main IF deck connector, plug and play,
without the addition of any new power transformers. Each of the twelve tubes in
the R-390 IF deck must be addressed for full compliance with the voltages
available from the R-390A. Refer to the schematic in Fig 1 as to the final filament
wiring configuration. We will also drop the B+ a bit.

Plug P112 of the R-390A shall be plugged-in to the R-390 IF deck at jack J517.

There is much commonality here, except for the connections mentioned herein.

In general, you will be converting 25V series connections into 6.3V (herein
referred to as 6V) parallel connections for most tubes, and moving the
connections of the BFO/PTO/ballast tube series to a different connection point in
jack J517. The 6V filament supply shall be provided to the R-390 deck by pin 20
of P112 from the R-390A.

General instructions: Refer to the schematic for the original R-390 as the "before"
schematic, and Figure 1 as the "after" schematic for filaments. Use the best
soldering technique you can in this limited access space. Don't insulate or bind
any wires until instructed to do so. You will be utilizing some of the new 6V
supply connections more than once. Make sure you can recognize your new
wires. I used black wire for the 25V supply, red wire for the 6V supplies, and
green wire for new grounds.

The first task is to install a B+ dropping resistor to better match the 180V B+
that the R-390 IF deck is expecting. To do this, locate inductor L503 under the IF
deck. This will be found snapped into a holder right above pin 2 of J517.
Disconnect one end of the coil, and install in series with it (the equivalent of) a
470 ohm 2 watt resistor. This will tame the B+.

The first tube circuit we'll work on is the ballast tube circuit.
IF deck tips                          page 285

V508 (5749) and RT512 (3TF7) These must be supplied by the R-390A 25V
filament supply. To do this, sever the connecting wire at pin 8 of jack J517
(underneath the deck) to free this slot up (hint: save access to the connector end
of the wire as you will use it to wire supply to V509). Then, sever the connection
at pin 2 of RT512 and wire this pin to pin 8 of J517 of the R-390
deck with a long piece of new wire. The filament return connection remains
unmodified. This modification will make the BFO/PTO/ballast tube series
connections identical to the R-390A 25V filament supply connections. As
mentioned above, this 25V supply is insufficient to supply the remainder of the
tube filaments, thus the need to employ the 6V supply for this task.

The following 6V tubes shall have filaments wired from the 6V R-390A supply.
The filament pins of these tubes are pins 3 and 4. Don't sever any connections
unless instructed to do so. The modification will use as much existing R-390 IF
deck wiring as possible (and thus may seem a bit screwy to you until finished).

V504 (6BJ6) 6V will come from its existing connection at pin 4. Ground will come
in the next step.

V503 (6BJ6) Wire pin 3 of V503 to pin 4 of V504 for 6V supply. Ground V503, pin

V502 (6BJ6) 6V supply will come from an existing connection at V503, pin 3.
Ground V502, pin 3.

V501 (6BJ6)Sever ground connection at V501, pin 3 and wire pin 3 to V502, pin4.

V505 (6AK6) 6V supply will come from existing connection at pin 4. Ground will
come in the next step.

V506 (6AK6) Ground pin 4 of V506. Wire pin 3 of V506 to pin 4 of V505 for 6V

V509 (6BJ6) Locate the free wire which was cut from underneath J517, pin 8, and
connect it to the 6V filament supply at J517, pin 20.

The following tubes are 12AU7's wired in various series schemes in the R-390.
They must be rewired according to their 6V option for use in the R-390A. Note
two of the connections require dropping resistors on the 6V source of V507 and
V510 to obtain the desired 5.3V filament voltage.

V511 Sever ground connection at pin 5. Connect pins 4 and 5 together for 6V
supply, ground pin 9.

V507 Sever connections at pins 4, 5 and 9, including the two resistors (one 120
ohm and one 22 ohm). Wire 6V supply from your previous work at V505,
through the deck opening for variable capacitor C525, to pins 4 and 5 through a
3.9 ohm, 1 watt resistor. Ground pin 9.
IF deck tips                            page 286

V 510 Sever connections at pins 5 and 9. Ground will come from existing pin 4
connection. Remove 120 ohm resistor between pins 4 and 9. Wire pin 5 to pin4.
Wire 6V supply from J517, pin 20 to V510 pin 9 through a 3.9 ohm, 1 watt

There are no changes to any of the other connections in the R-390 deck.

Prior to installing the modified R-390 deck in your R-390A, you must check your

Perform continuity checks from J517, pin 8, with RT512, pin 2.

Perform filament supply and ground continuity checks as follows. Note: There
will be more than one ground connection at various tube sockets, but the
filaments should have continuity exactly as shown.

Filament supply is checked from J517, pin 20.

V501, filament, pin 3; ground, pin 4.

V502, filament, pin 4; ground, pin 3.

V503, filament, pin 3; ground, pin 4.

V504, filament, pin 4; ground, pin 3.

V505, filament, pin 4; ground, pin 3.

V506, filament, pin 3; ground, pin 4.

V507, filament, pins 4 and 5; ground, pin 9.

V509, filament, pin 4; ground, pin 3.

V510, filament, pin 9; ground, pins 4 and 5.

V511, filament, pins 4 and 5; ground, pin 9.

Now insulate any bare connections, and use mini-tie wraps to secure the new
wires to sturdy nearby points. To enable final installation of the deck in your R-
390A, you'll need to make two adapter cables. These cables shall consist of
jumpers (RG-59 is OK, approximately eight inches in length) with BNC's on each
end. You'll also need two adapters of the type found on the back of the frame of
the R-390A at the IF OUT jack (AMPHENOL 47200). This will provide crossover
from MB connection (R-390A standard)to BNC (R-390 standard). Connect P-218
of the R-390A to J-526 of the R-390 IF deck with one of the cables. Connect P-213
of the R-390A to J-525 of the R-390 IF deck with the other cable. It is a good idea
to label these cables. See the photo for reference.
IF deck tips                                     page 287

Install the deck in your R-390A. You will notice that the screw holes are the same
as for the R-390A IF deck, however the screws of the R-390 deck are of larger
diameter. I did not change these screw as they are captive into the deck. The
BFO, BANDWIDTH, and power connector of the deck will hold it in place,
however I would not install it in a Jeep this way. Changing these screws is

When you turn on the power, make sure your dial lamps light up normally. If
they don't, you have a filament supply problem so turn off the set immediately
and troubleshoot.

For great sound, instead of using the built in audio deck, I prefer to tap the audio
from the diode load jumper at the back of the set. Through a 0.1 uF or larger
capacitor, feed this signal into your line audio amp of choice, and enjoy the tuned
circuit audio of the new R-725, errrr, R-390A with tuned circuit IF. You'll get the
smooth sound of the R-390 and R-725, but have the parts availability and support
common to the R-390A for the balance of the set. I've used my modified IF deck
in two different R-390A frames, and it worked equally well in both. In my
opinion, it makes the long term listening experience much more enjoyable. If
you have any questions about the mod, please feel free to write. References:

Cost Reduction Program for Radio Receiver, R-390/391( )/URR, L.W. Couillard,
Collins Radio, 1952.

TM 11-856/TO 31R1-2URR-154, RADIO RECEIVER R-390/URR, January, 1955.

Servo Corporation of America drawings for R-725 series 500 IF deck, Order No.
36-039-N-5-00093(E), September, 1965.


RECEIVER R-390A/URR, May, 1980.

Special thanks to Wally Chambers and George Rancourt.
IF deck tips                                     page 288

Date: Sun, 4 Feb 2007 14:50:08 EST
From: Flowertime01@wmconnect.com
Subject: Re: Transplanting R-390 IF modules to R-390A

It was not that the R390/A rang in the Radio Direction Finding System.The
system used a motor driven relay that switched the ring of antennas into the
receiver. the motor driven relay also provided a circular sweep signal for the
CRT display. The R390/A filters let a lot of hash noise from this switching unit
into the signal.

The R390 IF deck swapped into the R390/A receiver produced a cleaner display
than using a R390/A in the setup. The R390's were all tied down and were not
available to use. Folks with R390's were not even acknowledging that the even
existed. Radios or people. The R390/A were cooler than the R390/A. This was a
consideration in the air conditioned trailers most of the DF site people worked in.
Roger. AI4NI
Date: Sun, 4 Feb 2007 14:53:14 EST
From: Flowertime01@wmconnect.com
Subject: Re: Transplanting R-390 IF modules to R-390A

I had a lot of op's claim the R390 was a better CW receiver for working in the
Date: Wed, 7 Feb 2007 11:02:50 EST
From: DJED1@aol.com
Subject: [R-390] Strange modulation on carriers

I finished tweaking all the adjustments on my newly recapped IF stage and
started checking on the PTO runout. When I would tune through the calibrator
signal with BFO off I get a modulation, which varies somewhat with where in the
passband I tune. It's there for all bandwidths, and I'm not sure if it was there
before I took the IF module out. Strangely, it occurs on all the bands below 8
MHz, but not above. I assume it's modulation of the 17 MHz
oscillator, and will check it out when I remove the RF module for recap. Has
anyone seen a symptom like this? Any suggestions for troubleshooting it?
Other than that, the project is going as planned.
Date: Wed, 07 Feb 2007 11:34:14 -0500
From: "Tim Shoppa" <tshoppa@wmata.com>
Subject: Re: [R-390] Strange modulation on carriers

FM'ing of the 17 Mc oscillator, with the deviation strongly correlated to the AGC
action (thus you noticing it as you tune through the calibrator), is
commonlynoted. In my experience it is a few hundred Hz in the "bad" cases but
maybe it's more or less for you. It is partly a design flaw but for example a flaky
IF deck tips                                     page 289

17Mc crystal will be more pulled than a good strong 17Mc crystal. This is
probably at least one of the reasons why surplus 17Mc crystals are hard to find!

Some blame this on B+ regulation (or lack thereof) and this is possible too. You
can determine whether it's B+ regulation or AGC action by turning off AGC.

In one of my particular 390As, replacing R211 (which was high by several
hundred percent) and R209 (which was charred black) made the problem much
less evident. Yeah, I still hear some whoop-whoop on strong CW with AGC on,
but it's a reminder that I don't like AGC on CW anyway!

Unfortunately I did not independently replace R211 and R209 to see which one
was responsible for the fix. Yeah, guilty of shotgunning, but resistors that are
high by several hundred percent or already burnt to a crisp deserve a lot more
than a shotgun!
Date: Wed, 7 Feb 2007 11:06:32 -0800
From: "David Wise" <David_Wise@Phoenix.com>
Subject: 17Mc crystal (was RE: [R-390] Strange modulation on carriers)

Just to fill in some background, I believe that this is mentioned in the Cost
Reduction Report. The maximum frequency of crystals of the desired
characteristics had just passed 17Mc. They didn't want to use it, but other
considerations won. I'm working from rotted-out memory here; if anyone
knows the story more correctly, please follow up.
Date: Wed, 7 Feb 2007 14:53:54 EST
From: DJED1@aol.com
Subject: Re: [R-390] Strange modulation on carriers

Tim- Thanks for the information- at least I know I'm not dealing with gremlins. I
was going to pull the RF module anyway, so I'll check for burnt resistors. I've
got one spare crystal so I can try that also.
Date: Wed, 7 Feb 2007 15:31:40 EST
From: DJED1@aol.com
Subject: Re: [R-390] Strange modulation on carrier

Strange- I went down to the workshop to try a few measurements based on
Tim's suggestions. But in order to check performance without AGC I had to use
the signal generator, rather than the calibrator. Wow- no modulation at the
same signal levels. So it seems to be an interaction between the calibrator and
the 17 MHz oscillator. I reconfirmed that the modulation exists on the Cal
signal. Guess I've got a mystery to solve, unless someone has already done
that.          Ed
IF deck tips                                     page 290

Date: 13 Feb 2007 14:42:26 -0000
From: "n4buq@knology.net" <n4buq@knology.net>
Subject: [R-390] R390A Update

Many weeks ago, I posted some pictures of the replacement AGC capacitor:


I finally got around to reinstalling the IF deck into the radio and tested it. It
works great. Almost no differences in Carrier Level readings when switching
between the AGC settings.

Also, a few weeks ago, I asked about a good replacement for the 100-ohm
carrier-level pot. I had a 100-ohm ten turn pot, but the connection pins were
rather small and it was going to be a pain to mount the 22-ohm resistor along
with the other wiring. I started searching for another replacement and found a
20-ohm single-turn wire-wound pot made by Clarostat. This pot works fine and
eliminates the need for the 22-ohm parallel resistance. The drawback (it always
seems there's one) is it has 1/4" threads instead of 3/8" so you have to shim it
with some appropriate washers. It has a locking tab that doesn't match with the
original so you either have to shim it underneath, clip the tab off, or drill another
locking hole. I opted to shim it for now with some 1/4" stainless steel washers. I
plan to make an adapting collar for it that will accomodate the existing locking-
tab's hole and center the 1/4" shaft in the 3/8" hole, but for now it works fine.
Just thought I'd pass this along as another possible solution for the carrier-level
adjustment issue.
Date: Sun, 18 Feb 2007 14:32:59 -0500
From: "Jim M." <jmiller1706@cfl.rr.com>
Subject: Re: [R-390] Strange modulation on carriers

I have been chasing a whoop-whoop "chirp" on CW (with BFO turned on) heard
when received on this 390a, but not on the actual signals. The CW note would
tend to chirp on strong signals with AGC on. I measured the frequencies of all
oscillators with a calibration signal into the receiver, keying it on and off so the
AGC would jump. This caused the chirp, but it appeard to be the BFO frequency
that was being pulled with AGC, not the other oscillators. I noticed the B+ to the
IF stage varying a few volts with AGC action. (Changing AGC causes other
tubes to draw more or less current, hence causing slight fluctuations in the B+).
Changing out the 6BA6 BFO tube V505 reduced the chirp considerably. I believe
that the older 6BA6 tube may have been more susceptible to instability caused
by B+ variations. Jim N4BE
IF deck tips                                     page 291

Date: Sun, 18 Feb 2007 22:07:41 -0500
From: "Jim M." <jmiller1706@cfl.rr.com>
Subject: Re: [R-390] Strange modulation on carriers

More theorizing: I notice the pulling of the BFO frequency (causing the "chirp")
tends to be more noticable when the BFO is tuned very close to the signal
frequency in the IF (near zero beat). I have read of a phenomenon in older
radios where a very strong signal in the IF, coupling back into the BFO, can cause
the BFO to pull in toward the frequency of the strong signal (sort of a phase lock
effect). During the AGC attack time, a few milliseconds, the IF stages are still at
max gain resulting in a very strong IF signal coupling back into the BFO, hence
pulling its oscillation frequency slightly toward the strong signal. I notice this
only on one of the two 390a's I have here - in a Motorola IF module. If I tune the
BFO way off the signal (for a high pitch tone, or a BFO frequency further
removed from the strong signal), the chirp is less noticable. So if this is
happening I am not sure what the cure is, other than reducing the BFO coupling
capacitor (which is now 12 pf between the BFO tube and the detector tube) -
which would further reduce BFO injection and hurt product detector
performance. Some older "valve" receivers even ran the BFO at half the IF
frequency, using the 2nd harmonic for injection, to reduce pulling by strong
signals. Just some random thoughts.
Date: Fri, 09 Mar 2007 12:59:38 -0800
From: "Kenneth G. Gordon" <kgordon2006@verizon.net>
Subject: Re: [R-390] Mixer mod for 75A4 - possibly adaptable to the R-390?

<snip> BTW, ER also recently printed an article on a mod to the AGC system of
the R-390A. The result is an almost perfect AGC system with no overshoot, and
almost instantaneous rise time. It requires no added holes and only a few added
components. It makes the R-390A an extremely good SSB and CW receiver, yet
doesn't change its AM characteristics. The system and associated ideas are also
applicable to many other receivers. I'll try to dig out that one too.
Date: Fri, 09 Mar 2007 14:28:44 -0800
From: "Kenneth G. Gordon" <kgordon2006@verizon.net>
Subject: Re: [R-390] REALLY SNAZZY AGC mod for R-390A

> > > BTW, ER also recently printed an article on a mod to the AGC system
> > of the R-390A. The result is an almost perfect AGC system with no
> > overshoot, and almost instantaneous rise time. It requires no added
> > holes and only a few added components. It makes the R-390A an
> > extremely good SSB and CW receiver, yet doesn't change its AM
> > characteristics.
> > If you happen to scan any schemtatic of that, please share it with the 390 list.

The entire article is important. The schematic alone won't be of much help, as
there are things you must do that can't really be shown on a schematic. The ER
in question is Number 208, September 2006, page 30, entitled, "A High
IF deck tips                                     page 292

Performance AGC for the R-390A" and written by Clark Hatch W0BT of Topeka,
KS. Ray N0DMS the editor writes: "I have installed Clark's AGC circuit in my R-
390A and it is a "keeper"!. My receiver has been used almost daily for nearly 30
years and I highly recommend this modification because it is the best performing
AGC circuit I have ever used." In ER a few issues before this one, Ray published a
two part article on some upgrades and mods he had made to his own R-390A,
including one on a better AGC system. But Clark's works so much better than is
own, that he removed his, and installed Clark's. Ray shows an accompanying
test and a photo of an oscilloscope screen. When he switched his sig gen from Off
to On with a 0DB signal (224 mV) the rise time of the AGC system was measured
at 611 microseconds, and there is NO overshoot or ringing.

For a second test, he used a +20Dbm (2.2 Volts!) input signal. Rise time was
unchanged and total harmonic distortion was 4%.

Further, the annoying receiver blocking that occurs when switching from SLOW
to MEDIUM is gone because C-551 can no longer discharge into the AGC line.

The earlier articles also show o'scope photos of the ORIGINAL AGC system, and
there is really terrible overshoot and ringing.
Date: Sat, 10 Mar 2007 10:17:54 -0800
From: "Kenneth G. Gordon" <kgordon2006@verizon.net>
Subject: RE: [R-390] REALLY SNAZZY AGC mod for R-390A

> I've seen the articles and I have the receivers but I need to talk
> with someone who has actually done the mod.

I would suggest talking with Ray Osterwald, N0DMS. He is not only the editor of
ER, but is a very competent tech and VERY easy to talk with. The telephone
number for ER is on their website at:  http://www.ermag.com/

>One of my receivers was modified with what was to have been the best of the
>best mod but it works after a fashion with all the AGC and then some.

I don't understand this statement. Sorry. I DO know that there have been many,
many attempts to incorporate a really excellent AGC into the R-390 series. Some
work better than others, some aren't really any better than the original, and
some are actually worse. However, Clark Hatch's appears to be a real winner.

> > I use 390As. in fact I got rid of my 51j-4 and the R-725 beats it hand
> down. Question is have you modified any units relative to the two
> articles involved?

Not yet, but Clark's is certainly on my list. I have a really excellent R-390A which
one of our list members sort of traded to me a while back, which I have never
yet turned on since I don't want to lose any filters. I intend for that one to
become my main station receiver. Now, many years ago, I DID modify the AGC
system in an R-390A to my satisfaction for use when doing AFMARS phone
IF deck tips                                     page 293

patching into Vietnam, and I have also modified an R-390 by adding a triode
product detector to it. I used 1/2 of that dual triode which ordinarily feeds the IF
out to a jack on the back, so I didn't add any holes or extra tubes. It made a big
difference in recovered audio and signal-to-noise ratio on SSB.
Date: Wed, 14 Mar 2007 21:50:55 -0600
From: "Barry" <n4buq@knology.net>
Subject: [R-390] Distortion in MGC on strong signal

When tuned to strong stations in MGC mode, my R390A is driven into
distortion. Monitoring the Diode Load, I'm seeing approximately -60V when
tuned to a strong station. Backing the RF Gain control to where the Diode Load
reads more around -30V causes the signal to sound normal again. Switching to
AGC (any AGC speed) causes the Diode Load to drop to about -30V and the
signal sounds normal as well. I can reduce the IF Gain to almost zero and cause
the Diode Load in MGC mode to be around -30V with the RF Gain at "10", but
I'm sure this is too low of a setting for the IF Gain Control. I've followed the
manual's procedure (150mV into the IF deck and set for -7V Diode Load) as well
as backing it off slightly for Chuck Rippel's procedure so setting i far enough
back to keep the Diode Load down to an acceptable level when the RF Gain is at
"10" is not the correct solution. I assume the radio should not be acting this way,
right? If not, any suggestions on where to look for problems?
Date: Wed, 14 Mar 2007 23:17:27 -0400
From: "Jim M." <jmiller1706@cfl.rr.com>
Subject: Re: [R-390] Distortion in MGC on strong signal

My radio is also driven into distortion in MGC unless I back off the front panel
RF gain. What you describe seems to be normal behavior on strong signals.
Things work much better with AGC on, that's why there is an AGC circuit. In
fact I leave my AGC on all the time.
Date: Thu, 15 Mar 2007 05:58:58 +0000
From: eldim@att.net
Subject: Re: [R-390] Distortion in MGC on strong signal

I find that this seems to be NORMAL BEHAVIOR for any receiver that operates
without an AGC circuit, with the audio being distorted in the presence of strong
signals. Thank goodness for AGC, for without it you would always have to
fiddle with the RF Gain Control to deal with varying signal levels. I do find the
MGC Mode to have it's advantage when trying to pull in very weak signals. My
nickels worth.
IF deck tips                                     page 294

Date: Fri, 23 Mar 2007 14:04:28 -0400
From: "Bob Young" <youngbob53@msn.com>
Subject: [R-390] R-390A selector problem

On my Motorola 390A I have an intermittant problem: with the 4,8 and 16 KHz
filters the sensivity is good, when I switch to 2,1 and 0.1 the S meter drops about
50 db with corresponding volume loss. This is intermittent however as it will